Patisserie 11: Fraisier/Sponge Cake with Strawberries and Mousseline

I wasn't intending to make this cake until strawberries came into season, usually in May. So I planned to make the biscuit moka and the Opera and then move onto the macarons section. However, for the biscuit moka, a quantity of dark rum was needed, and I had a feeling that brushing these delicate cakes with whiskey like I had been using as a rum substitute up until now would not be the best plan. But I also don't really drink dark rum and didn't want to buy a bottle just for the few tablespoons I'd need, here and there. So I called up my friend Kevin, a rum enthusiast that I had not seen for a while, and we met up for dinner (at a delightful Italian restaurant called Bottega that had just opened a week ago on Valencia St). On our way back to his place for me to pick up some rum, we saw the woman who is often at 21st and Capp Streets, on the corner under the light of a streetlamp, selling boxes of fruit. 

Among these were boxes of strawberries. Kevin immediately suggested we buy some. "Are her strawberries good?" I asked, skeptical. 

He replied, "Her strawberries are the best." 

And that's how I ended up with a half cup of rum and a pound of strawberries that evening, and plans to make the fraisier cake the next day. 

The Fraisier is a classic French layer cake (I hesitate to use traditional because I tend to apply that term to things with cultural significance outside of cooking, rather than just part of a culinary tradition) that usually involves strawberries and some form of cream, sandwiched between layers of sponge cake that are brushed with a (usually spiked) syrup. It derives its name from fraise, which means strawberry in French. 

The recipe in The Book is unusual (or perhaps just simple) in a few ways: 

• No form of whipped heavy cream is involved (either Chantilly or Diplomat); this recipe uses mousseline instead.
  
• The inner strawberries are left whole, rather than chopped or turned into a compote
• The top layer is torched French meringue and a glaze of apricot jelly, rather than a layer of marzipan or the recently popular additions of a thin layer of strawberry gelee over a thin layer of the same cream as used in the filling. 

In the introduction to the section on cakes, The Book points out that "French cakes are not the dramatic high-risers of American diners." So I guess it makes sense that their design for their Fraisier is not a tall cake with standing strawberries in cross-cut profile, piled high with cream and wearing many layers of topping. Instead, the recipe is an understated affair that simply highlights the red color of the strawberries under the warmth of torched meringue, and the cream and cake colors fade into the background. 

I began by making the pastry cream because it would need to be chilled completely before incorporating into the mousseline. I have stopped taking photos of the process at this point because I've made it quite a few times already and documented it at length on this blog. Once that was in the fridge, I started on the biscuit (sponge cake). 

A sponge cake, in its simplest form, continues the trend of using only egg components as leavening agents. In comparison to the dacquoise from a few weeks ago, a sponge cake does also start with the egg whites whipped with sugar until firm, but then the egg yolks are added back in and wheat flour is also folded in. I sifted the flour while the egg whites were whipping.

Whipping egg whites for the sponge, with the yolks to be whipped in later and the flour sifted and ready to fold in

Once the egg whites had incorporated all of the sugar and were holding stiff peaks, I added the egg yolks and let the mixer whip them in as well, yielding a final texture that was somewhere just past a soft peak.

Egg yolks whipped into the egg whites

I folded in the sifted flour as two additions with my silicone spatula, trying not to work the batter too much but also trying not to leave many streaks.

Flour folded into the sponge cake batter

In order to make sure I was able to achieve the 12"x8" final dimensions of the cake as stated in the recipe, I did something I thought myself quite clever for coming up with. I set my adjustable cake rectangle to the final dimensions, set the frame on my sheets of parchment, traced the outer dimension with pencil firmly on both sheets, and then placed the sheets upside down on the baking trays. This allowed me to see the outline of the shape I was aiming for as I spread the batter.

Planning ahead by tracing out desired dimensions of the cake for spreading batter! On the left is the parchment as traced, on the right is the parchment flipped so the pencil marks are against the baking sheet and won't touch the cake batter

The batter, when divided between the two rectangular shapes, spread out to be about half an inch in height, and I was barely able to get it uniform enough to cover all the edges. Because the recipe had me using the spatula to spread from the beginning, I was hopeful that I wouldn't cause any undue deflation if I was gentle.

I had barely enough batter to make an even layer on both marked rectangles

After I popped the first cake layer in the oven to bake at 350deg F with convection fan on, I realized I had neglected to sift a layer of powdered sugar on top of the batter, and did so promptly with the remaining layer.

Oops, forgot to add powdered sugar to the first cake layer

I baked each layer for a total of 12 minutes, rotating the baking sheet once at the halfway mark. The cake layers came out uniformly light brown and, much to my surprise, held their height after baking (and even puffed up a bit in the oven!). This is in stark contrast to both my batches of dacquoise, which deflated by about a third of their height after baking. The confectioner's sugar on the second sheet had turned into a thin, crackly membrane, much like the outer surface of a meringue. I brought both sheets onto racks to cool.

The cake layers browned very gently and evenly, and did not deflate (and maybe even rose a little bit)

Once the sheets were cool, I used the cake rectangle to trim the edges, leaving the cake layer I liked the least (the one without the sugar dusting, somewhat arbitrarily) in the rectangle to serve as the bottom layer of the cake. 

The recipe calls for kirsch to be used in a sugar syrup that is brushed over the cake layers. I am somewhat confused why many of these cakes seem to be dry and then require a syrup soak, but maybe that is the nature of a cake with so little fat. Nonetheless, I was loathe to acquire a quantity of a fairly niche liqueur, so I used some of the Cocchi Americano Aperitif I had in my cocktail stash. I was considering whether to use elderflower liqueur, but decided that the herbal mishmash in the Cocchi Americano, along with its slight bitterness, would lend enough of a floral touch and that the elderflower might be a little too loudly itself. 

I dissolved the sugar in water over the stove, allowed it to cool, and stirred in the Cocchi Americano. I brushed it liberally over the bottom cake layer in the rectangle but stopped once I had even coverage. I hadn't made a cake like this before, and I did not know how much syrup it could handle before it turned to mush; The Book mentions that the recipes make more than I would need, but that I could brush with as little or as much as I liked, but to not "drench them," whatever that means.

Cut and weeded cake layers, with the bottom one fitted into the rectangular pan for assembly and brushed with the alcohol sugar syrup.

I then set to work on the buttercream, which is also lacking in photos due to the number of times I've now made it. I did, however, get to the bottom of an important discrepancy that I had run into before, and that would cause trouble in this recipe. 

The Book says that this recipe makes approximately 5 cups, or 1000g. Typically, the volumetric quantity has been the estimate throughout the recipes in this book, and the weight in grams is the actual basis. However, I found that when I finally weighed the entire quantity of this buttercream in order to reserve half of the batch for a later recipe, the recipe had only made 800g. This explains why I had less than expected after reserving some of my previous batch for the Paris-Brest! And, at this point, while I was nervous about filling the entire cake rectangle given my 4/5 quantity of buttercream, it was too late to try and make more now, and I set aside 400g for later and powered through with the 400g I had left.

This is half of the recipe of buttercream, but the recipe claims it makes 1000g, so I've been shorting myself some buttercream all along.

It was nearing 80 degrees F in my house on this uncharacteristically warm day in SF, and, remembering my past experience with buttercream losing structural fluffiness when warming, I decided to stick the buttercream into the fridge to firm up some more before I returned to assemble the cake. 

In the meantime, I hulled the strawberries. Usually, I cut a little cone out of the top instead of just lopping the top off because I think this is pretty wasteful, but for sake of the aesthetics of the ends of the strawberries pressed up against the sides of the cake, I went with the method stated in The Book as pictured. Some of these strawberries were also on the more unripe side, so I guess I was not losing that much as I chopped off the white parts. I placed them roughly in order from largest near the top of the tray to smallest near the bottom, and I cut some of the largest ones in half so they wouldn't disturb the uniform height of the cake when assembled.

Hulled strawberries in a slightly inefficient way for aesthetics, and sorted from largest to smallest, cutting the largest ones in half in the top of the photo so that they wouldn't make parts of the cake higher than others

I returned to my slightly-colder buttercream and whipped it back up while I stirred 150g of the chilled pastry cream to eliminate any lumps. Finally, I whipped the pastry cream into the buttercream for the mousseline. The Book mentions that a tablespoon of pistachio paste is an optional addition, but I both a) accidentally bought a pistachio paste from the store that had sunflower oil and sugar and a bunch of other things added so I didn't trust the flavor, and b) did not want to begin making a mess with my food processor for a whole batch of the paste only to use 1tbsp of it. So I just left it out, and I am not sure I missed it.

Re-whipping the chilled buttercream and smoothing out the pastry cream to be whipped in for mousseline

I spread two thirds of the cream into the rectangle on top of the bottom cake layer, though in retrospect I should have maybe only done half. It's becoming clear that my rectangle, while nice for its adjustable size in case my cakes don't come out to the full size of a standard pan, is a little too deep for spreading things in. Even an offset spatula will have issues as the handle runs into the opposite rim of the pan. Mostly it's difficult to move things from left to right in the pan, so I've settled for making sure the filling gets evenly dolloped from left to right, and then it's easy to spread out from the center towards the long edges.

Two-thirds of the mousseline spread onto the bottom layer of the cake

I arranged the strawberries in a single layer and nestled them into the mousseline by pressing gently. I placed the strawberries on the edges first, placing the whole ones almost next to each other and turning them so they faced the edge of the rectangle before pushing them down. The remainder of the strawberries, halved or otherwise, tessellated so well into the center of the pan that I was surprised.

A shockingly well-packed layer of strawberries

Here is where that last 100g of buttercream might have come in handy. I had a really hard time trying to get even coverage with the last third of the mousseline. It flowed into the nooks and crannies between strawberries and, coupled with the awkwardness of maneuvering the spatula in a too-deep pan, made it really hard to spread without disturbing the strawberry layer. I think it looks better in the photo than it really was, but the mousseline was gone so I didn't have a choice but to proceed.

I ran out of top-layer mousseline and had a hard time distributing it across the cake without disturbing the strawberries.

I deposited the top cake layer with the strategy I used in the dacquoise, where I left the weeded cake layer on the parchment, flipped it upside down into the rectangle, pressed it onto the rest of the cake, and then slowly peeled the parchment off at an aggressive acute angle, keeping my hand behind the parchment for a clean peel. The sponge stuck a little to the parchment and left behind a thin but continuous layer on the parchment. But most of it made it into the pan, and I brushed it with almost all of the remaining syrup, imagining that the top would not have as much issue if it became less structural, and that the filling of the cake would be able to handle a little extra syrup. I snugged up the edges of the pan against the cake and put it into the fridge to chill for about two hours, to give the mousseline a chance to set.

Topped up the cake and brushed most of the rest of the syrup on top!

I made myself a nice low ABV cocktail by topping up the remaining Cocchi Americano sugar syrup with sparkling water, which I sipped while enjoying the toasty weather. When about an hour and a half had passed, I started working on the thin layer of French meringue to be spread on top of the cake. I whipped the weight equivalent of two egg whites (60g) with granulated sugar until there were stiff peaks, and then folded in sifted confectioner's sugar. It was actually quite difficult to fold in the powdered sugar because of how little meringue there was in comparison, but eventually I got it all. I spread it as evenly as I could on the chilled cake, knowing that the torching process would highlight any surface imperfections.

Did my best to spread the French meringue evenly without ripples on the top of the chilled cake...

And then it was time once more to use a blowtorch! The meringue browned readily and I worked in slow rows.

...and as expected, the torching amplified every ripple. Not too bad, considering I was trying to use an offset spatula to smooth the surface more than an inch under the top of the pan

When I was preparing the apricot glaze, I made a big mistake. The grocery store near my is too fancy to stock sugary, clear apricot preserves, and the brand I bought simply...had too much fruit in it. This is normally not a complaint, but for the sake of patisserie, apricot preserves are often strained to use the clear jelly as a relatively flavor-neutral, glossy finish. When I heated up the preserves with some water and realized how little glaze there would be and how much would be chunks of fruit, I decided to try pureeing the mixture with an immersion blender and then straining out the fruit bits. 

The fruit absolutely pulverized and made my glaze cloudy, and could not be strained out. Luckily, the thinness of the layer I poured onto the meringue and spread about helped keep it mostly translucent, and the peach color did lend a warmth to the top that brought it away from brown and more towards amber. The translucency also helped even out some of the uneven browning from ripples in the meringue, so, no harm no foul.

My accidentally-cloudy apricot glaze actually mellowed out the appearance and added some gentle color.

Finally, it was time to demold the cake. I pulled the ring upwards and the cake slid out easily. Ta-da! If I cared more, I could clean up the side strawberries, and you can see that the meringue was much thicker on the edges, but the beautiful ratio of cake to strawberries to cream (surprising, since I ran out of top mousseline), along with the pillowy white meringue layer and the glossy brulee, made for a stunning cake. I stuck it back in the fridge for another hour before cutting and serving any.

Not the flattest cake, but beautiful nonetheless

And here's the cross-section cut! I was very concerned about cutting this cake, because the minefield of whole strawberries inside seemed to spell out doom for a tidy cut. But, much to my surprise, a slight sawing with my sharp chef knife was all it took to make clean cuts through all the strawberries. The cake was soft and did not stick to the bottom parchment, and the slices held their shape well enough to deposit into various tupperwares of my friends that I called for reinforcement in helping eat this cake (it is supposed to be eaten within two days of assembly).

Look at that set mousseline! That glossy meringue layer! Those strawberries nestled tightly in the cream! The melt-in-your-mouth sponge! I'm pleased with myself!

Thoughts: 

• I have very few complaints! I think this cake is a faithful reproduction of all aspects of the recipe!
• This made a lot of cake. Even though this was smaller than the succes praline, I gave away at least two slices to four different people and we still had a fair amount left for the house. Good thing it's easy to eat.
  
• I think the presentation went great! As I've struggled with presentation in the past, I'm really glad this turned out basically picture perfect with the reference photos.
• Maybe the one thing is the buttercream being short. I think it would be really annoying to try and do 1.25x the recipe, so maybe I will just take 500g portions whenever I need "half of a recipe of buttercream" and split the other 300g into a 200g and 100g, and eventually I'll be able to put together another 500g from odds and ends of the next recipe. It's a good thing buttercream freezes well.
  
• I couldn't really taste any of the soaking syrup, which is fine; I'm not sure kirsch would have added much, but I do think I would have liked a little more flavor from the syrup, so maybe elderflower would be a nice addition next time. 
• Speaking of syrup, I noticed that the cake layers, while not dry anymore, did seem to only have obvious syrup penetration about halfway through. While I don't want to make the layers completely within the territory of a moist, dense pound cake, I do think I could have sloshed even more syrup onto them. 
• The strawberries were quite good! And I liked them even more the day after, when they had a chance to soften a bit and meld their flavors with the cake. 
• The meringue layer on top is great, and several people mentioned that it added a lot. While it's fairly sweet, it's like a mini dessert counterpoint to the slight tartness of the strawberries. 
• The mousseline was amazingly light. I feel like I did not need the earthy nuttiness of pistachio. 
• The entire cake was so easy to eat and well-ratio'd! In combination with the unexpectedly warm day, it's like summer has already arrived. It is just asking me to eat slice after slice...
  

 Quotes of the day: 

<Cake is too pretty. Not going to be the one to cut it> -Ryan

< cake is not quite as pretty anymore but it is incredibly tasty> -Kai

-From our house groupchat, as Kai facilitates eating of the cake through commendable self-sacrifice of eating the first slice of the remainder

"That cake is one of the best-tasting things I've ever eaten. Definitely professional quality." -Ryan, after he finally ate some cake. He is being very nice to me and my baking, even though it is making him have to work out more.