"I feel the end approaching.
Quick, bring me my dessert, coffee and liqueur."
- Pierette, great-aunt of Anthelme Brillat-Savarin

2 1/4 cups well-chilled heavy cream
3/4 cup confectioner's sugar, sifted
1/2 teaspoon vanilla extract
3 tablespoons Cognac
1/4 cup chopped lightly toasted slivered almonds
3/4 cup chopped toasted and skinned hazelnuts
6 ounces bittersweet chocolate, chopped fine
1 ounces unsweetened chocolate, melted and cooled
3 tablespoons Grand Marnier
2 teaspoons unsweetened cocoa powder

Make the spongecake: In a metal bowl beat together lightly the eggs, the granulated sugar and the vanilla, set the bowl in a large pan of hot water,
and stir the mixture until it is barely warm. Remove the bowl from the pan and with an electric mixer beat the mixture for 10 minutes, or until it is tripled in volume. Sift the flour over the egg mixture in batches, folding it
in gently, and fold in the butter gently, 1 tablespoon at a time.
Butter a jelly-roll pan, 15 1/2-by-10 1/2-by-1 inches, line it with wax
paper, and butter and flour the paper. Turn the batter carefully into the
pan, spread it evenly, and bake it in a preheated 350-degree F. oven for
17 minutes, or until it is golden. Let the spongecake cool in the pan on a rack, invert it onto a cutting board, sprinkled lightly with confectioner's sugar, and peel off the paper.
In a chilled bowl beat the cream until it just holds soft peaks, beat in
1/4 cup of the confectioner's sugar, the vanilla, and 2 tablespoons of
the Cognac, and beat the mixture until it just holds stiff peaks. Fold in
the almonds, the hazelnuts, and the bittersweet chocolate, transfer half
the mixture to another bowl, and fold the unsweetened chocolate into
the mixture in one of the bowls.
Line a 2 1/2-quart bowl with 2-inch-wide strips of wax paper. Cut the spongecake into pieces and cover the wax paper with some of them, reserving the remaining cake for the top.
In a small bowl combine the Grand Marnier and the remaining 1 tablespoon Cognac and brush the cake lining the bowl with the mixture, reserving 2 teaspoons. Spread the vanilla cream mixture on the side of the spongecake and spoon the chocolate cream mixture into the center. Cover the cream with the remaining spongecake with the reserved liqueur mixture. Chill the dessert, covered with plastic wrap, for at least 6 hours and up to 24 hours. Invert the dessert onto a serving plate, discard the wax paper, and sprinkle the dessert with 1/4 cup of the remaining confectioner's sugar.
In a small bowl combine the remaining 1/4 cup confectioner's sugar with
the cocoa powder. Cut out 1/4-inch-thick strips from a sheet of wax paper, put them over the dessert to make ribs", and sift the cocoa sugar over the dessert. Remove the wax paper carefully and chill the dessert.