When I was young, my bonnemaman (french for grandmother) would make a mocha cake whenever my parents and I would come to visit. Unlike American Mocha, the traditional European (or maybe just Belgian) is just coffee flavored. It was an excellent cake, that both my parents and I have very fond memories of. Unfortunately, no one ever got the recipe from my grandmother. We do, however, know some of the elements. The frosting was a coffee flavored buttercream, which she added texture to by including granulated sugar. The trouble with this is that most buttercreams can hold very little liquid, and so just adding coffee to a buttercream won’t make a frosting, and extracts don’t provide the same flavor. My grandmother also had a philosophy that when the frosting contained as much fat as hers did, the cake shouldn’t contain any fat, and so she used a genoise with no butter added to it. Based on this I set about trying to construct a version of the recipe. Finding a genoise recipe was easy, I used the one from Bakewise. The frosting recipe was more complicated, but then my mother found a recipe for a Flemish crème-anglaise based coffee buttercream, which she sent to me. Armed with these two recipes I decided to take a shot at it. Of course, I have nothing to do with a full cake, so instead I made the cake in a jelly roll pan, and turned it into petit-fours. I made 1 ½ times the genoise recipe, and half the frosting recipe, which ended up with my making way too much cake, and way too little frosting. My genoise was also far from perfect, the first attempt failed utterly (I underbeat it massively), and the second, while a vast improvement, was far from perfect (the flour was not evenly mixed). I have reprinted the recipes here in the proportions I made them, you might want to adjust accordingly (this is also why a lot of the measures in the cake are strange).
So how did they turn out? Pretty good I would say. The cake itself definitely reminded me of my grandmothers, though it wasn’t quite there. I thought the frosting was a little too buttery, but this might have been because the butter ended up far too soft when I put it in, and so it might not have fluffed up as much as it would have otherwise. I also didn’t add any granulated sugar to the frosting, and it really could have used that added texture, as both the frosting and cake are very tender. I did add espresso beans to the tops of the cakes, which added some much needed contrast.
Simple Genoise
Makes one 11 x 17 jelly roll pan (at least, mine was probably overfilled)
9 large eggs, in the shells1. Arrange shelf in the lower third of the oven. Preheat to 350 degrees. Grease and flour an 11 x 17 inch jelly roll pan. Line with parchment, grease the parchment
2. Put the eggs, in their shells, in a bowl and cover with very hot water. Mix together the flour, the 1 ½ T sugar, the cornstarch, and the salt.
3. Put two inches of water into a skillet over medium heat. Separate three of the eggs, placing the yolks in the bowl of your mixer. Add the remaining 6 eggs and the remaining ¾ cup sugar. Place the mixing bowl into the skillet of water. Whisk the mixture constantly until it reaches between 86 and 9 degrees.
4. Attach the bowl to a mixer set with the whisk attachment. Beat on high for two minutes, and then reduce speed to medium and beat for another 10 minutes. Mixture should be thick and foamy, and should fall in thick ribbons from the whisk.
5. Sift ¼ of the flour mixture over the egg mixture. Gently fold the flour into the egg, repeat in 4 to 5 batches until all of the flour is incorporated. Gently fold in the vanilla.
6. Pour the genoise batter into the prepared pan. Bake for 10-12 minutes, or until puffed and golden. The center should spring back to the touch. After removing the cake run a knife around the edges so the cake can settle.
Coffee Buttercream
1/3 cup espresso coffee beans
1. Coarsely crush the espresso bean in a mortar and pestle processing in small batches so that none of the coffee is crushed finely. Combine the crushed espresso beans with the milk in a small saucepan and bring to a simmer. Remove from the heat, cover and let steep for 10 minutes. Strain through fine sieve, pressing down on the beans to extract as much milk as possible. You should have about 1/3 of espresso-flavored milk. If necessary at a little milk to get back up to 1/3 cup. Discard the coffee grounds and rinse out eh sieve so it will be ready to use again for straining the custard.
2. Combine the espresso-flavored milk with 2 T of the sugar in a heavy 1 quart saucepan and bring to a simmer.
3. Meanwhile, combine the egg yolks with the remaining sugar in a mixing bowl and beat with a wire whisk until smooth and lemon-colored. Pour in about half of the hot milk, whisking constantly. Pour this mixture back into the saucepan and stir until thoroughly blended.
4.* Place the saucepan over medium heat and stirring constantly with a wooden spatula, stirring the custard almost to a simmer. Reduce the heat to low and cook, stirring constantly with the spatula until the custard thickens and coats the spatula heavily. (When you draw a line across the back of the custard-coated spatula with your fingertip, the custard should not flow back over the line). Reduce the heat to the lowest possible setting (moving the saucepan to the side of the burner as needed) and keep the mixture hot, again stirring constantly, for 4 minutes to pasteurize it. – This is the original instruction, and I hate instructions like this, I cooked mine to 175 degrees, which was nice and thick, but not overdone.
5. Immediately strain the custard through the fine sieve into the bowl of the mixer. Beat the custard with the wire whip at medium speed until is light and cool. This is the buttercream base.
6. Gradually beat in the softened butter at medium speed, using the flat beater if your mixer has one. When all of the butter has been added, beat the buttercream vigorously to make it as light as possible.
7. Use the butter cream right away.
Assembly
Cake
1. Cut the cake into 1 x 2 inch rectangles. Slice each rectangle of cake in half horizontally (so that you now have two layers).
2. Generously put about a tablespoon of frosting between the two layers. Press together. Use a butter knife to spread a thin layer of butter cream over the outside of the cake (this is the crumb coat, it doesn’t need to look great). Refrigerate the cakes until firm, which will take several hours, or place in the freezer for about 10 minutes.
3. When the crumb coat is firm, use a butter knife or offset spatula to apply a second layer of frosting. I’m not great at this, so have no tips here.
4. Top the completed petit-fours with espresso beans, or other decorations.
