Patisserie 13: Opera/Glazed chocolate and coffee layer cake

 We've arrived at last at one of the most ambitious cakes in patisserie: The Opera Cake, or Gâteau opéra. From Wikipedia: 

It is made with layers of almond sponge cake (known as Joconde in French) soaked in coffee syrup, layered with ganache and coffee,...French buttercream, and covered in a chocolate glaze. Its namesake originates from the layers resembling the levels of an opera theatre

 This cake is meant to be decadent yet delicate, with umpteen variations on its many layers making it a popular cake that presents nicely when sliced to reveal its layers. The version of the cake in The Book has three cake layers, two butter cream layers, a layer of ganache, and a layer of glaze, for a total of six. 

 I knew that this cake would be a doozy of a time commitment, so I divided the process between two days, baking the cake layers on the first day and returning to assemble the next day. 

The cake in an Opera is a Joconde, which is a hybrid between a biscuit/sponge cake (whipped egg whites and yolks subsequently added) and a Genoise (eggs are whipped whole for the batter). In the Joconde, whole eggs are whipped, and extra whites are whipped separately and folded into the batter to lighten it further. This recipe used a whopping eight eggs as a result, with four whipped whole with the four remaining yolks, the ground almonds and, sugar.

Ingredients for the joconde, including eight eggs

The egg batter is whipped at high speed for fifteen minutes (!!) until it lightens and becomes very ribbony.

A long whip for the egg batter

Because I would be dividing the batter into three layers, I weighed the amount of batter so I could have even cake layer weights.

Weighing the egg batter to make it easier to divide across three pans later

I whipped the four separated egg whites from earlier with the rest of the sugar to create a French meringue, and weighed it as well after adding it to the batter. In retrospect, I'm sure folding in the meringue caused me to lose some weight as the air escaped, so it may have been better to weigh the egg white after it was folded in.

Weighing the egg white meringue to aid in division

Finally, some flour is folded into the batter. As with the Mocha cake, I was fascinated at how the batter became noticeably more structural and tough as soon as the flour began to get folded in and the gluten began to activate, compared to the dacquoise or other almond flour-based cakes which create a smooth batter with no resistance that is constantly threatening to deflate.

Finally, flour folded into the egg components

I set each pan on my scale and decanted a third of the batter by weight onto each pan, and, after spreading the first one into an even layer, I tried to match the dimensions while spreading the other two sheet pans so my cake layers would be roughly the same size. I spread the layers until they were roughly 8mm thick.

Batter divided by weight across three sheet pans, and spread to about 8mm thick, leaving a 1in border on all sides, just about

I was not watching the oven closely enough and browned the first cake rather severely. Considering this recipe is supposed to make a 12"x16" full sheet pan, and none of my cake layers came close to that size, I'm kind of surprised my layers cooked so quickly (though many of the other recipes have also been a little short on final dimensions when I execute them). You can see the progression in the color of the cake layers as I pulled them earlier and earlier, trying to match the photo of the cake layer in The Book. While the Book says "10-12 minutes", I ended up around 9 minutes for each layer, rotating the pan once in between.

This could be a modern art triptych titled "Iteration"

At this point, I let the cake layers cool, then stacked them, parchment and all, and wrapped them in plastic wrap to chill in the fridge overnight. 

I also prepared the coffee syrup used to soak the cakes, as well as the strong coffee used for flavoring the buttercream, and let them sit at room temperature overnight.

The next day, I began preparing the assembly structure. I cut and weeded the cake layers, which had softened somewhat in the fridge and were easier to cut sharply without crumbling the edges. I would like to digress for a moment and extol my decision to get an adjustable cake ring. While it has made beautiful assembly a little difficult because the additional height interferes with the movement of the offset spatula, I have been absolutely pleased with my ability to adjust the cake dimensions based on the actual baking size. The Opera cake layers yielded 10.5"x13", which is a nonstandard cake ring size, and had I been using a standard one, I would be wasting a lot more cake scraps. 

However, to deal with the aforementioned height problem, because the Opera cake is shorter even than many other French cakes (which is nonintuitive, considering how many layers there are!), the Book recommends making a base out of cardboard to take up the half inch of height in the pan. Not knowing how my cake would stack up (harhar) in terms of final height, I decided to make a cardboard base to the same dimensions as my cake layers but also add additional height by wrapping up a quarter sheet pan with two cutting boards underneath the base.

Made up a platform to take up space in the cake ring underneath the cardboard base, using more cardboard and two cutting boards

I then fit the cake ring around my franken-platform, for a final height of roughly two inches within the cake ring.

Cake ring fitted over the base

The first cake layer I left on its baking parchment, in order to provide a barrier between the cake and the cardboard. I folded the parchment down along the edges, using the cake ring to keep it in place.

First cake layer, still on parchment, aligned with the cardboard base and snugged up with the cake rectangle

Now, I've mentioned before how much I hate working with chocolate. The Book mentions that the percentages of chocolate called for in each recipe are fairly exact, because the cacao to butter ratio will affect the behavior of the chocolate. The ganache in the Opera recipe called for 60% cocoa; the glaze called for 52%. And I was unable to find any couverture that met either percentage, so I settled for the next best thing, which was to get some 46%, 55%, and 63%, and buckle down to do some math.

These were my chocolate percentage options, and also I cheaped out and got the fanciest baking brand instead of couverture

I had to dig pretty deep for my arithmetic knowledge to create a system of equations for each of my required percentages of chocolate, using the expected cocoa weight of the full weight, as well as the percentages I had on hand. And you can see I'm already getting rusty at my day job old job, based on the number of corrections I had to make to my math. But eventually I had my final proportions by weight for how much of each type of chocolate to mix in order to obtain the final percentage of cocoa by weight called for in the recipe.

I'm kind of embarrassed at how many mistakes I made in this math. Can't believe baking has got me out here making goddamn systems of equations...

To make the ganache, I measured out the proportions of the 55% and 63% necessary to achieve the final percentage of 60% in 170g of chocolate, and chopped it up. Cutting chocolate chips and walnuts are the only reasons I strongly desire a slapchop, and it's baffling to me that there isn't a better method of chopping chocolate chips that I've discovered yet. At least I can buy walnut bits pre-chopped in the store.

I hope I did my math right.

I mixed cream and milk in a saucepan, brought it to a boil, and then poured it into the chocolate, and added the butter and mixed until I got a smooth ganache.

The cream and chopped chocolate in preparation for making ganache

I also brought out the buttercream I reserved from the mocha cake and re-whipped it until light, adding the strong espresso from the day before at the end to flavor it. With my coffee syrup, coffee buttercream, and chocolate ganache all ready, it was time to begin layering. As usual, the cake layer gets brushed with an egregious amount of the coffee syrup.

Clockwise from bottom: first cake layer brushed with syrup, coffee syrup I made ahead, remaining cake layers, emotional support dining table objects, espresso buttercream, chocolate ganache

Next, I spread roughly half of the buttercream over the first cake layer. I noticed I was barely able to get even coverage, which alarmed me, especially since I thought I had made a point to reserve as much buttercream as the recipe called for in grams. If you recall, I found out earlier that the recipe in The Book makes about 800g, rather than 1000g, but subsequent recipes that call for half of the buttercream recipe reiterate that they require 500g.

Half the buttercream spread onto the bottom layer

But I pressed on the second cake layer as soon as the buttercream covered the entire first layer. This second layer also got a dousing in coffee syrup. I used the most browned cake layer for the middle layer, figuring that it could do with the additional moisture availability from being sandwiched between the buttercream and the ganache.

Put the most-baked layer of cake down so it could absorb stuff from both sides, being in the middle

Next, I spread the ganache on top. I was again alarmed, this time at the way the ganache seemed to be absorbing into the cake! I was at first concerned that I had too much ganache, but upon application and absorption, it became apparent that I had just enough to create a concrete layer of chocolate above the cake.

The ganache both wanted to escape off the sides and absorb directly into the cake layer, even though the cake was already full of syrup

After some squaring of the edges of the cake rectangle to corral the ganache, I set the third and final cake layer on and brushed it with the remaining coffee syrup. I could see at this point that I should not have doubted The Book's estimation on the final height of the cake being 1.25"; I had almost an inch of clearance between the top of the cake and the top edge of the pan.

The last cake layer, brushed with the rest of the syrup. In brushing, I seem to have created a table dressing as a homage to Pollock

It was a warm afternoon, and I noticed the buttercream wilting, so I stuck it in the fridge and re-whipped it after it had cooled. You can see the very obvious difference between the light whipped buttercream and the dark wilted buttercream on the edges. I learned my lesson from the mocha cake that buttercream just really needs to be whisked into oblivion to work right.

I learned my lesson from the Moka and let the buttercream chill before rewhipping to full glory before application. You can see the darker, unwhipped buttercream is quite obvious in contrast to the fluffy, light colored buttercream of correct texture.

I basically ran out of buttercream while trying to frost this last layer and had to get really clever with redistributing. This is unfortunate because this layer is pivotal for the smoothness of the final cake, because the thin chocolate glaze is supposed to be able to flow smoothly and not pool thicker at some points than others. That's also why it would have been better for me to get less clearance between the top of the pan and the cake, because it would be easier to smooth the buttercream into a flat layer. I'm concerned that I keep running out of buttercream in all of these recipes (save for the first dacquoise, where it didn't really matter how thick I made the buttercream layer). After this point, I may as well start making a whole quantity of buttercream for each recipe that calls for half, and just use the remaining buttercream to make fairy bread.

Why is the buttercream always gone?

The cake went into the fridge to chill for two hours (and it was hefty at this point! I was concerned I'd drop it!). I returned in the evening to prepare the chocolate glaze. Mixing my afore-calculated ratios of the 46% and 55% chocolate to achieve 400g of 52% cocoa concentration, I mixed this with vegetable shortening and grapeseed oil and set it all over a pot of simmering water to melt together. The oils do the double duty of preventing the chocolate from setting too hard and giving a glossy sheen to the glaze; I assume the heat absorbing capacity of oil also helps the chocolate keep its temper. I did accidentally overheat the chocolate slightly (it was very difficult to clip the candy thermometer to the bowl).

Mmm, delicious oily chocolate bits

The final glaze seemed liquidy enough, and I allowed it to cool until it was the temperature that I was supposed to have heated it to.

The texture of the glaze while hot

I pulled the chilled cake out of the fridge and gingerly removed the base layers propping it up. The edges were fairly cemented to the cake ring, and I used the old hack of a hairdryer to warm up the sides of the cake ring until I could pull it up vertically with ease. It is very tempting to make the edges of the adjustable ring bigger to extract the cake, but I've noticed it makes for unclean edges and may also bring along more cake than I'm comfortable with along for the ride.

The revealed cake after chilling and cake ring/base removal! Not too bad, it's reasonably flat

I poured all of the chocolate glaze on top and smoothed it as best as I could, stopping as soon as I noticed it was starting to retain my spatula marks for too long. I think it was respectably flat, despite how lumpy my cake was. The whole thing went back into the fridge to chill for another hour until the glaze was set.

Smoothed the chocolate glaze as best as I could and set it back in the fridge to chill for a few more hours and set

I trimmed the edges off to both neaten the sides of the cake and prevent anyone from getting an uneven distribution of components, as tends to happen along the sides. To cut the cake, I stuck my knife in a narrow, tall vessel filled with hot water for a few seconds until the metal heated up, then, after drying the knife briefly with a towel, placed the blade on the cake and allowed it to melt through the glaze, then cut the layers of the cake as normal. Drying the knife between soaking and cutting is essential; water will look incredibly bad if it comes in contact with chocolate.

The first slices of cake! Distinct layers, chocolate cut reasonably, cake held together when transferring to plates/tupperwares

Despite my chocolate math, I'm pretty sure something went wrong with the chocolate glaze. It remained fairly stiff when I was trying to eat it, when I think it was supposed to be more of a soft, forkable texture. Maybe this is related to my choice of chocolate chips rather than purer couverture, and also due to my overheating it? Similarly, the ganache layer seemed to absorb a fair amout into the cake layer underneath. Overall, though, I think the cake came out well, even if the layers are not as distinct as I would have imagined. While the chocolate was powerful, the coffee was also powerful, and there was a surprising balance in that sweetness that was aided by the volume of the cake layers.

I need to get better plating and shots of the final products

Some thoughts:

• I continue to find working with chocolate an inscrutable task.
  
• Due to the syrup, there wasn't an appreciable difference between cake layers baked too long, which was useful to find out.
• There were definitely places where the chocolate glaze was thicker than others, causing the ratio of chocolate to cake to be a little disruptive. This could be better with a few of the points I mention below (enough buttercream to smooth, and a lower cake ring).
  
• What is up with the buttercream quantity! At first I thought I maybe wasn't whipping it enough, but even letting it go for the full ten minutes, it hasn't appreciably increased in volume past the point I've used it at so far. I guess I'm just going to have to double buttercream and use 1.5 times what the recipe calls for, and then reserve the rest for a later date. 
• I'm really glad I split this between two days, and as the summer months approach, I'm certain I'm going to have to spread recipes over even more days to keep components cool and in workable condition. 
• If I'm to continue making cakes like this in the future, I do wonder if it's worth investing in a 12x10" cake rectangle that's less tall. I think I'll try some of the recipes from the Curley book and then decide what the quantity of cake I prefer to make is going to be, and then buy a rectangle to suit that. 
• This cake was not as difficult to make as I imagined! It did have many components, but I'm looking forward to riffing on those as distinct flavor profiles in the future. The syrup, the buttercream, and the ganache could all be independently adjusted, and I understand now why this is a popular cake for variations on flavor. 
• ...But my life is not ready for this much cake. This made a lot of (intense and decadent) cake, and it took over a week for it all to get eaten, even after I gave away more than half of it to various friends and their roommates. Likely it would be easier with fruit flavors, but there's only so much buttercream one can eat comfortably...
  
• I'm going to have to sort out getting a replacement fridge for the house soon if I'm going to continue down this road (and eventually make this honey cake that needs umpteen counter and storage space) due to the multi-day assembly and slower consumption time nature of cakes.

My next set of lessons is going to be macarons, which I enjoy eating but have also heard are difficult to master, and as someone who's had some truly disgusting macarons, I hope I don't have to eat too many mistakes before I figure out a workable method for me.