A dacquoise is a meringue cake layer, usually a mix of beaten egg whites and ground nuts. Here (of course), it’s turned into something like a Parisian pastry chef’s version of a sheet cake. Before you get started, please note that the dacquoise layer requires three hours in the oven, then at least 1½ hours to cool completely at room temperature. Afterwards, you’ll top it with a true French buttercream, a frosting made from egg yolks and butter, a true bit of dessert decadence fit for any occasion.
For the dacquoise
Unsalted butter for the parchment paper
3 cups confectioners’ sugar
2 cups finely ground toasted skinned hazelnuts
2 cups finely ground almonds
12 large egg whites, at room temperature
¾ cup granulated white sugar
1. Position the rack in the center of the oven and heat the oven to 250°F. Butter a 13 × 18-inch lipped sheet pan, line it with parchment paper, then generously butter the paper and the inside lip of the pan. Stir the confectioners’ sugar and both ground nuts in a large bowl until uniform.
2. Using a handheld electric mixer or a stand mixer with the whisk attachment, beat the egg whites in a second large bowl at low speed until foamy, then increase the speed to high and beat until you can form soft peaks, 3 to 4 minutes.
3. Add the white sugar 2 tablespoons at a time, beating at high speed all the while, until thick and glossy. Scrape down and remove the beaters or whisk. Using a silicone spatula, gently fold in the nut mixture just until uniform throughout without deflating the egg whites. Spread the mixture over the parchment paper in the sheet pan, a moderately thin layer lip to lip.
4. Bake until firm to the touch without browning, about 3 hours. Cool in the pan on a wire rack to room temperature, about 1½ hours. (Do not even start the frosting until the cake layer is at room temperature.)
For the buttercream
6 large egg yolks, at room temperature
¾ cup granulated white sugar
½ cup dark corn syrup
32 tablespoons (4 sticks) unsalted butter, softened to room temperature
8 ounces dark chocolate, preferably 70% cocoa solids, chopped, melted and cooled to room temperature
1. Using a handheld electric mixer or a stand mixer with a whisk attachment, beat the egg yolks in a large bowl at medium speed until light and thick, about 3 minutes. Set aside.
2. Combine the sugar and corn syrup in a medium saucepan. Set it over medium heat and cook, stirring occasionally, until the sugar dissolves. Bring to a boil undisturbed; boil for 1 minute.
3. Beating all the while at medium speed, drizzle this sugar mixture into the egg yolks. Continue beating at medium speed until the mixture is fully room temperature, 10 to 15 minutes. Test it by cupping your palms around the outside of the bowl and by turning off the beaters to stick a clean finger right down into the mixture in several places.
4. Beat in the softened butter in 2-tablespoon increments, working slowly but steadily and efficiently. Beat in the chocolate until uniform. Spread and smooth the buttercream over the cooled dacquoise. Serve at once or cover lightly with plastic wrap and store in the refrigerator for up to 1 day.
TESTER NOTES
Look for skinned and roasted hazelnuts at most large supermarkets. Some large markets even carry ground hazelnuts.
