French Opera Cake

Instructions

1. Prepare the Joconde Sponge
   Preheat oven to 425°F (220°C). Line two 9x13 inch baking sheets with parchment paper. In a clean bowl, beat egg whites until foamy, then gradually add granulated sugar and beat until stiff peaks form. In a separate bowl, mix almond flour and powdered sugar, then beat in the whole eggs until light and fluffy. Gently fold in the flour, then the melted butter. Finally, fold in the egg whites carefully to maintain volume. Divide batter between the two pans, spreading thinly and evenly. Bake for 7-8 minutes until light golden. Let cool completely.
2. Make Coffee Syrup
   Combine hot espresso or strong coffee with coffee liqueur (if using). Set aside to cool completely. This will be used to moisten the cake layers.
3. Prepare Coffee Buttercream
   Dissolve the instant coffee powder in 1 tablespoon hot water. In a large bowl, beat the softened butter until creamy. Gradually add powdered sugar, beating until light and fluffy. Add the dissolved coffee and beat until well incorporated and smooth.
4. Make Chocolate Ganache
   Place chopped chocolate in a heatproof bowl. Heat heavy cream until just beginning to simmer, then pour over chocolate. Let stand for 1 minute, then stir until smooth and glossy. Allow to cool until spreadable but not too firm.
5. Assemble the Cake
   Cut each cooled sponge sheet into three equal rectangles. Place one rectangle on a serving plate. Brush generously with coffee syrup. Spread a thin layer of coffee buttercream over the soaked cake. Top with another rectangle of cake, brush with syrup, and spread with chocolate ganache. Add the third rectangle, brush with syrup, and spread with buttercream. Repeat the layers, finishing with a rectangle of cake on top.
6. Add Final Glaze
   Prepare an additional small batch of chocolate ganache if needed. Pour over the top of the cake, spreading evenly to create a smooth, glossy surface. Refrigerate for 10 minutes until set.
7. Decorate and Finish
   Using a hot knife (dipped in hot water and wiped dry), trim the edges of the cake to create clean lines. For traditional decoration, pipe the word 'Opéra' on top with remaining buttercream or ganache, or dust with cocoa powder. Refrigerate for at least 2 hours or overnight to set completely.