Preheat the oven to 450F. Lightly grease a 17x11 jelly roll pan and line it with parchment; grease the paper (alternatively, use a Silpat and grease the mat).
Using a stand mixer fitted with the paddle attachment, beat the almond flour, confectioners’ sugar, all-purpose flour, whole eggs, and egg yolk until combined. Stop to scrape down the sides of the bowl as necessary.
In a separate bowl, whip the egg whites and fine sugar with an electric hand mixer until a thick, glossy meringue forms. Gently fold the meringue into the almond mixture. Add the melted butter and gently fold again, being careful not to deflate the batter. Pour into the prepared baking pan; spread evenly using an offset spatula. Bake for 5-7 minutes, or until the cake springs back when pressed in the center. Remove from the oven and let cool slightly. The cake should pull away from the sides of the pan, but if it doesn’t, run a knife between the cake edge and the pan to loosen the sponge.
Invert the cake onto a wire rack and carefully peel away the parchment or silicone liner. Conservatively trim away the browned edges of the cake using a small sharp knife. Set aside to cool completely.
Stir together the espresso powder and 1 tablespoon of the water. Stir until dissolved. Add the remaining water to a saucepan along with the granulated sugar. Bring to a boil and stir until the sugar is melted. Remove from the heat and stir in the espresso and brandy or cognac. Let cool to room temperature.
French Coffee Buttercream
Stir together the espresso powder and 1 tablespoon water until the powder is dissolved. In a saucepan, bring the sugar and remaining water to a boil, stirring until the sugar is dissolved. Clip a thermometer to the side of the pan and bring to a boil without stirring. Wash down any crystals that may form on the sides of the pan using a pastry brush dipped in cold water. Cook, and bring to 238°F (soft ball candy stage) and remove from the heat.
Beat egg yolks in the bowl of an electric mixer fitted with the whip attachment for 1 minute. With the mixer running, add the hot sugar syrup to the yolks in a slow fine stream (avoid getting the syrup on the sides of the bowl, aim for the middle). Add the dissolved espresso mixture and beat at high speed until completely cooled. The mixture may look liquid and not at all like buttercream. This is normal. When the mixing bowl is cool to the touch, switch to the paddle attachment and, with the mixer running, add butter pieces one at a time. The mixture may begin to look curdled – this is normal, keep going. When all of the butter has been added beat on high speed until the mixture comes together in a thick, creamy mass of silky buttercream. Cover and set aside.
Chocolate Glaze and Topping
In a large microwave-safe bowl, melt the butter and 6 oz. of the chocolate together (reserve remaining 2 tablespoons/1 oz. of chopped chocolate), about 1 to 1 minute 30 seconds in a standard household microwave. Use a whisk to gently stir the mixture smooth. Add the remaining 2 tablespoons of chocolate and whisk until melted. Let stand at room temperature until thickened to spreading consistency, or speed setting by refrigerating. Stir the mixture often if refrigerating.
Assemble the Cake
Cut the cake evenly into thirds (I recommend using a ruler). Place a layer on a serving plate and use a pastry brush to apply an even layer of the coffee syrup. Spread half of the French buttercream over the soaked sponge. Top with a second layer of sponge and brush it with the coffee syrup. Spread half of the chocolate glaze over the soaked sponge. Top with the remaining sponge cake and brush with coffee syrup. Add the remaining French buttercream and spread to the edges. Chill the cake until the buttercream is firm, about 30 minutes.
Reheat the remaining chocolate glaze in the microwave for about 15 seconds or until shiny and pourable but not hot. Pour the glaze over the top of the cake and spread evenly. Chill until firm.
When the cake is firmed, trim away the edges of the cake to neaten. Cut slices evenly into fingers (about 2 inches wide). Decorate as desired, gold laurel instructions follow.
Modeling Chocolate Decors
Heat the chocolate chips in the microwave at full power in a microwave-safe bowl at 30 second intervals, stirring thoroughly after each heating. When the chips are smooth, add the corn syrup and stir until the mixture becomes thick, the chocolate with lose its shiny appearance. Spread the mixture on a large piece of wax paper and top with a second sheet; gently roll flat with a rolling pin. Let stand until firm 1-2 hours.
Remove paper from the surface and knead the chocolate until pliable and puttylike. Press small pieces of the chocolate clay into the candy mold until overflowing. Use a knife to trim the excess chocolate away so that the chocolate in the mold is flat and even with the mold’s surface. Freeze for 10 minutes. Remove gently and let stand until room temperature. Repeat until you have as many laurels as you have cake pieces (about 5-6).
Dip a dry art brush into luster dust and gently brush over the high points of the decorative laurels. Add a dot of corn syrup to the backs of the laurels and attach to the tops of the opera cake slices. Refrigerate cake until ready to serve. Bring to room temperature before serving.
Adapted from Epicurious.com, the Sprinkle Bakes book, and other textbooks on classic French pastry.
Keyword french pastry, instant espresso powder, layer cake, opera cake, patisserie