Chocolate-Lover’s Cake

To make the cake: Lightly coat the insides of two 9-inch round cake pans with some of the melted butter. Line each pan with waxed or parchment paper, then lightly coat the paper with more melted butter and set aside. Preheat the oven to 325 F.

Melt the 1 cup of butter and the semi-sweet chocolate in the top of a double boiler over barely simmering water, stirring until smooth. Set aside at room temperature.

Place the egg yolks and sugar in a medium bowl and beat until the mixture is slightly thickened and pale in color, about 4 minutes. Scrape down the sides of the bowl and beat for 2 more minutes.

Place the egg whites in a large clean bowl and beat until stiff peaks form. Using a rubber spatula, fold the melted chocolate mixture into the beaten egg yolk mixture. Add one fourth of the beaten egg whites and stir to incorporate, then gently fold in the remaining egg whites.

Divide the batter between the prepared pans, spreading it evenly, and bake in the preheated oven for 45 to 55 minutes, or until a toothpick inserted in the center comes out clean. Remove the cakes from the oven and let cool in the pans for 15 minutes. During baking the surface of the cakes will form a crust; this crust will collapse when the cakes are removed from the oven. Invert the cakes onto wire racks. Remove the paper and let cool to room temperature, then chill in the refrigerator for 1 hour.

To make the mousse: Melt the chocolate in the top of a double boiler over barely simmering water, stirring until smooth. Remove from heat and set aside at room temperature.

Place the heavy cream in a deep bowl and beat until stiff peaks form. Set aside. Place the egg whites in a large clean bowl and beat until soft peaks form. Add the sugar and continue to beat until stiff, glossy peaks form. Whisk one fourth of the whipped cream into the melted chocolate. Fold the chocolate mixture, then the remaining whipped cream, into the egg whites gently but thoroughly. Cover and refrigerate.

To make the ganache: Heat the heavy cream in a medium saucepan over medium-high heat. Bring the cream to a boil, stirring so that it does not boil over onto the stove. Place the chocolate in a heatproof bowl and pour the hot cream over the chocolate. Cover the bowl with a plate and let stand 5 minutes. Stir until smooth; set aside at room temperature.

Chop the hazelnuts to 1/4-inch pieces using a pulsing action in a food processor, or chop by hand. Do not use a blender. Combine 1-1/2 cups of the chocolate ganache and 1 cup of the chopped hazelnuts in a medium bowl and set aside at room temperature.

To assemble and decorate the cake: Remove the cake layers from the refrigerator. Place one of the cakes on a cake plate or decorative cardboard cake circle and spread the hazelnut ganache evenly over the cake top. Reverse the other cake layer and place it right side up on top of the ganache-covered layer; press the layers together gently. Using a very sharp serrated knife, trim the top and sides of the cake so that they are even. Refrigerate for 30 minutes.

Remove the cake from the refrigerator and spread 3/4 cup of the chocolate mousse evenly over the sides of the cake. Chill the cake in the freezer for 30 minutes, or refrigerate for 1 hour.

Remove the cake from the freezer and place on a wire rack set in a baking sheet. Pour the room temperature ganache over the cake, spreading it evenly with a spatula to cover the top and mousse-coated sides of the cake. Refrigerate the cake for 20 to 25 minutes to set the ganache.

Transfer the remaining chocolate mousse to a pastry bag fitted with a large star tip. Remove the cake from the refrigerator and pipe mousse stars over the entire top of the cake. Press the remaining chopped hazelnuts into the ganache on the sides of the cake, coating the sides evenly. Refrigerate the cake for at least 1 hour before cutting and serving.

To serve: Cut the cake with a serrated slicer, heating the blade under hot running water and drying it between each slice. Allow the slices to come to room temperature for 10 to 30 minutes before serving.