Patisserie 12: Biscuit Moka/Mocha Cake

 The moka cake is the first "advanced" recipe I've tried from the cakes section of The Book. At first, it was not immediately apparent why this recipe was marked as being harder than the other cakes, because in comparison, the assembly is a lot easier and there are fewer components overall: a sponge cake (similar to the Fraisier from last time), coffee buttercream, and toasted almonds. I suspect the difficulty rating is due to the risks of baking a tall, circular sponge cake, and also in part due to the assembly process of the final cake. But I think, for my first cake of this form factor, that it all went well. It is an atypical shape of cake because it is apparently an Alsacian festive cake, and various flavor profiles can be used. This recipe used rum and coffee as the chief flavorings.

Like in the Fraisier sponge, this sponge cake began with egg whites separated from the yolks, to be whipped into stiff peaks with sugar. However, instead of beating the egg yolks into the meringued whites, the egg yolks were also beaten separately with sugar until they were pale and thick. Additionally, the cake contained flour but also the addition of corn starch. I sifted these two powders, though I perhaps should have sifted them together as well. Back in the day, sifting was important to prevent unsavory milled things from getting mixed in with your flour, but now, it's primarily done to eliminate lumps that will either remain undissolved in the batter and bake up as little raw flour pellets, or necessitate additional folding to incorporate that risks overworking the batter and either deflating it or creating excess gluten formation that will make the cake tough.

The ingredients for the sponge: Egg whites ready for whipping, egg yolks and sugar to be whipped simultaneously, more sugar to whip into the meringue, and flour and cornstarch sifted together.

While I let the stand mixer do its thing to the egg whites, I whisked the egg yolks together with sugar as a comrade in arms to my mixer. I used a dish towel underneath my whisking bowl to keep it from moving around, and I had to take a few breaks (under the guise of checking on the status of the egg white peaks) because my arm was getting very tired! Truly my stand mixer is the undisputed VIP of my baking still, after all these years. But eventually, we had glossy, stiff peaks in the stand mixer and thick, pale egg yolks, ready to combine. 

It's worth noting that the ingredients for the batter all eventually go into the egg yolk mixture, so it's important to start with a medium or large bowl to accommodate the folding of a full quantity of batter. 

Whisking away by hand and by machine

Here is the batter once the egg whites are folded into the whipped yolks. It has deflated very little, and I should think it's good to keep it that way.

Whipped separate eggs folded together into the bowl

I incorporated the flour in three batches, but found it to be fairly streaky. By the end of the third batch, as I was scraping the bottom of the bowl to make sure I hadn't missed any spots, I was beginning to feel the heaviness of the flour resisting my spatula, even though the batter had not deflated all that much. I decided it was better to quit while I was ahead and not worry about any more streaks. This is one of the reasons I think it may have been good to do a second sifting of the flour and cornstarch once they were both sifted separately, because together the mixture might be less willing to clump upon contact with moisture.

Flour and cornstarch folded into the whipped eggs

I had earlier prepared an 8" round pan (2" high) with 3" strips of parchment for lining that I cut off of the ends of one of my pre-cut sheets (one from the long edge, one from the short edge). This left me with enough parchment to rest underneath the round pan and serve as its bottom barrier against the sheet pan I was to bake everything on. I gently shoveled the batter out of the bowl and into the round pan, and I used the back of my mixing silicone spatula to smooth out the top without depressing too much lest it deflate. I didn't bother using an offset spatula here, because I knew it would be a pain to flatten the surface of the batter given the parchment rising up on either side. The batter came up to the top edge of the round pan, but I trusted that the parchment height would keep the sides of the cake in order.

The batter came up to the two-inch height of the cake circle, and I hoped the parchment would do its job.

This cake was then baked at 350deg F for "at least 20 minutes" with convection heat until lightly browned. This is the only recipe thus far to not give an upper bound for the cake baking, which was a little concerning. When I checked the cake at 20 minutes of baking time, one tap of the sheet pan revealed that the center of the cake seemed quite jiggly. In my experience, tall cakes like this struggle to cook all the way through evenly (this is why Bundt cake pans and angel food cake pans have that hole in the middle, to avoid this problem!), but where in a regular cake I might lower the temperature or drop the convection heat, I knew this cake would be brushed in syrup, so I was not concerned for it to come out dry. I let it bake for another 7 minutes, and by the time I pulled it out, the top was springy when gently pressed, and the center was no jigglier than the rest. The cake had also not browned excessively.

The cake was rather tall when I pulled it from the oven, exceeding the height of the parchment, and several medium-sized cracks had developed on the top surface. But I was glad the parchment paper had held its own and kept the sides of the cake straight. I moved the cake to a rack to cool and slipped the cake ring up and off easily, and once the cake had cooled enough to touch, I peeled off the parchment from the perimeter.

The cake immediately after leaving the oven. It was quite tall!

I kept checking on the cake as it cooled, because it began to sink almost immediately. One of the reasons, I think, why this cake is "advanced" is because of the tendency of tall, round sponge cakes like this to sink in the middle. 

There are a few reasons why cakes might sink, either as they bake or as they cool, and these troubleshooting tips are well documented on various websites and books. The biggest dangers for the sponge cake composition in this recipe were probably: 

• Oven temp (too cool - cake won't set before air bubbles escape. Too hot - cake will be cracked and peaky, but then the outsides will cook way faster than the inside and the cake will collapse once cooled)
• Underbaking (if the batter is not set, it cannot hold the tiny bubbles in its structure)
• Overmixing (deflated batter will not be as airy because the egg mousse matrix is the only thing providing leavening in this cake, and too much gluten formation will create a tough cake)
• Undermixing (not enough gluten formation will also make it hard for the cake to maintain structure, though the recipe said to mix until just combined so I think it's unlikely this was a large concern for this type of cake)

I think working with the dacquoise early on has more than wizened me up to the dangers of overworking a meringue batter, so I continue to be extremely careful when folding in ingredients. While the extra time on the baking probably meant my cake was not underbaked, I did have to open the oven to jiggle the pan, and ideally that would be unnecessary.  But on the plus side, the cracks that had opened up on the top of the cake had disappeared due to the top sinking, and my overall sinking was quite little, resulting in only a slight concavity by the time the cake was at room temperature. Not bad for a first attempt! Unfortunately, The Book does not provide a reference photo for how the cake should look once cooled before cutting, so I have no metric by which to visually evaluate the sinkage of the cake.

Completely cooled cake. There is a little sinking in the center, but overall the cake is a reasonable cylinder.

While I waited for the cake to cool enough to cut, I first ate lunch, and then brewed a stronger-than-usual coffee in my 2-serving Moka pot, which just meant packing two whole tablespoons of coffee into the canister. I poured three tablespoons of this into a bowl and dissolved a teaspoon of instant coffee into it and let it cool. The Book calls for either espresso or strong coffee, and given that a Moka makes something almost as strong as espresso on the continuum of coffee strength, it seemed like a better option than to try and brew stronger coffee with pourover. 

I would like to shamefully admit at this point that I certainly do not drink enough coffee to have fresh coffee on hand at all times, and I used one-year-old pre-ground cold brew coffee, which was very good when I first bought it, and I had been using it periodically when making coffee for myself. The instant coffee was also very old Folgers (though I don't think it suffers with age, mostly because it's not that impressive to begin with and there's nowhere lower for it to go, really). But I drank the remainder of the coffee in my Moka and it tasted...like coffee, as usual. I don't know! I am not picky about my caffeine flavors! (unless it is west coast third wave coffee, with its "fruity acidity and tart berry notes and stone fruit" i.e. sourness and inexplicable mapping to soy sauce aroma in my brain...but that's a tirade nobody agrees with)

I placed the cake on a quarter sheet pan and gingerly cut it in half with a serrated bread knife, using the edge of the pan as a rough guide to keep my cut planar. I think I did...okay, though my knife could have been sharper. The cake was very spongy, as the name might suggest, such that a wire cake cutter probably would have been unable to successfully cut through the elasticity. I was relieved that the interior of my cooled cake was completely cooked, and the edges seemed to be as uniformly cooked as the center. I'm chalking this up as a moderate success!

Sponge cake is...spongy. I don't know what I expected.

Having seen the dangers of trying to frost a not-quite-cool cake, I let the newly opened cake layers rest for a bit while I worked on the rest of the recipe. I brought out the reserved half recipe of buttercream from earlier in the week from the fridge, and dropped it into the stand mixer to whip for a few minutes. When it had achieved light, fluffy volume and a very pale color once more, I poured in the cooled coffee flavor from earlier. The buttercream broke briefly, and I scraped down the sides to make sure all the coffee got incorporated, but another minute of whipping brought the buttercream back together and perhaps even a little fluffier than before!

I brushed the cakes with a syrup made of sugar dissolved in warm water, cooled, and then with rum added. Since these layers were kind of thick, and I knew from the last cake that the sponge would be fairly dry once baked and would likely be able to handle more moisture, I used up all the syrup, split between the two cut faces of the cake. 

Sponge cake layers brushed with syrup, and coffee buttercream being whipped in the stand mixer

The recipe states to use slightly less than half the buttercream for the bottom layer, but because I knew the amount of buttercream I started with was lower than expected (due to the discrepancy I discovered last time where the recipe for buttercream yielded about 200g less of the 1000g stated yield), I wanted to err on the side of excess for frosting the surface of the cake. So I used about a third on the first layer, spreading gently with an offset spatula.

I was sparing in the first layer of buttercream that I spread on the bottom layer of the cake, because it would be far worse to run out of exterior frosting than to have a little thinness between layers.

I placed the second layer on top with the cut side facing up. You can see here that there is barely any noticeable sink in the center by this point.

Second layer of the cake assembled atop the first, with the cut side facing up

I then used another third of the buttercream and smoothed it across the top of the cake, letting excess coat the sides as it fell.

Top of the cake as flat as I could make the buttercream

Finally, I used about 2/3 of the last third to frost the perimeter of the cake. This was a little harder to do smoothly, both because I don't have a way to keep the spatula at a constant angle to the cake, and because the cylinder isn't completely even. I did a first rough pass just to get most of the large gaps filled in, and then came back with more buttercream to try and get coverage of all cake surfaces.

Pretty ok! I was not adamant on a smooth outer face because I knew I would be covering this with almonds later on.

Facing the camera on the center right of the top edge of the cake, you can see a slight depression. This is from one of the blobby edges of the sponge top sinking in, such that when turned upside down, it created a large gap. I filled it in the best I could with buttercream, but it's not a very structural icing. But I straightened all the edges as much as I could and sent the cake into the fridge to chill for a little over an hour to let the buttercream set.

The divot on the top edge just right of center is due to the way the cake sank and pulled the edges in with it. I tried to patch it with some buttercream, but there's only so much structure you can build with mousse...

The recipe asks to keep the remaining reserved buttercream at room temperature, but it was approaching 75 degrees in my house today, so I stuck it into the fridge. When it was time to do the final pass on the top of the cake, I brought it out and whisked it lightly by hand. This was a mistake; the color was noticeably darker and I was unable to incorporate nearly as much air as was necessary for a glossy, smooth finish. I spread the reserved buttercream on the cake, but when I went to draw the bread knife patterns across the surface, the buttercream became ragged due to the large air bubbles, instead of being smooth in the undulations. 

I had toasted some almonds per the recipe for ten minutes at 350deg F at the beginning of the recipe, and it was time now to use them as decoration on the sides of the pan. The Book contains an audacious photo of the entire cake being held up in the left hand while a spatula first smooths the sides and angles of the cake, and then presses almonds into the sides of the cake. I had no illusions about my likelihood to immediately get my thumbprints all over the cake and ruin the mouse, and probably subsequently drop the entire cake, so I took the slightly less convenient but safer approach of pressing patches of almonds into the sides of the cake while it rested on the sheet pan. I scooped up fallen almonds carefully as they dropped to use in other areas, and as a final touch, I placed choice almond slices around the top of the cake and also stuck them on one by one in areas that looked too bare.

I left the cake on the pan and pressed toasted almonds to the sides, and did a final pass manually sticking almond slices one by one into gaps that remained, as well as along the top edge to try and create a sharper profile.

After chilling in the fridge for another hour, the cake was ready to cut. I used my chef's knife as before, but found that this cake was much more resilient to cutting, possibly because the sponge layers were so thick and springy (true to name!). Running the knife under hot water to heat it up and then drying it seemed to make the cuts cleaner, though there was nothing to be done about any almonds caught up in the cutting path and immediately getting knocked off of the cake.

Here's the cake interior! It's kind of uniformly brown, not the most beautiful cake inside. I understand why the Book only has shots of the cake exterior...

The cake was exceedingly hard to photograph because of the similarity in colors between the cake, buttercream, almonds, and parchment (I notice that the Book only contains photos of the cake as a whole and does not show any interior shots). This is the best I could do; you can see that the syrup clearly has soaked into the top half of each layer, that the middle buttercream layer is a little thin, and that the cake has mostly kept its shape through slicing.

My best attempt at showing the layers. You can see the halfway point on each cake layer where the syrup soaked to, the thin middle buttercream, and the slightly thicker upper buttercream.

Thoughts:

• I'm so glad I trusted my gut on the wobbling cake and left it in the oven for longer, though I think it will be better for me to use this timing rather than risk opening the oven next time I do this recipe
• The middle buttercream layer was a little scant, and I think having the full 500g of buttercream would have helped fill that out more.
• Using all the syrup was perfect, we got about halfway through each cake layer and it was not lacking in moisture or too soggy.
  
• I should whip the top buttercream reserve properly in the mixer before spreading it, the improperly whipped texture was very noticeable in the visual product. 
• I wonder what untoasted almonds would contribute to the flavor. There's a floral quality to them when they're raw that might work better for a chocolate or fruit flavored version of this cake. 
• Because the sponge was ever so slightly concave, I might have tried leveling off the top before cutting the cake into layers. 

Quote of the day: "Another masterpiece, Helena. But it kind of reminds me of popcorn." - my friend and housemate Steven, who found the combination of butter and nuttiness from the toasted almonds to cross some wires in his head. To his credit, he also liked the cake, despite not liking the flavor of coffee.