Night and Day Cake ►

To prepare the chocolate cake: Preheat the oven to 350 F. Lightly butter and flour a 10-inch round cake pan. Sift the cornstarch, cake flour, and cocoa together. Beat the egg whites and lemon juice at high speed until soft peaks form. Sprinkle in the sugar and continue beating to firm peaks. Slightly beat the egg yolks and fold into the whites. Gradually fold in the dry ingredients, being careful to preserve the volume of the egg whites. Pour the batter into the prepared pan and bake for 30 minutes, until the sides of the cake pull away from the pan slightly. Remove from the oven and let cool 10 minutes; turn out onto a wire rack and let cool completely. Brush off any crumbs.

To prepare the ganache: Melt the chocolate in the top of a double boiler over barely simmering water. Whisk in the butter. Set aside.

To make the syrup: Bring the sugar and water to a boil. Remove from heat and cool. Add the rum or Grand Marnier. Set aside. This syrup will keep indefinitely in a covered jar in the refrigerator.

To prepare the white chocolate mousse: Melt the chocolate in the top of a double boiler over barely simmering water. Set aside. In a small pan, combine 2-1/2 ounces of sugar and 1/4 cup of water and cook to 248 F (hard-ball stage). In a round-bottomed mixing bowl, combine the egg yolks, whole egg, teaspoon of sugar, 1 tablespoon of the dark rum, and the Grand Marnier. Set the bowl over a pan of warm water (about 160 to 170 F) and constantly beat the mixture until it is warm and foamy. Add the dissolved gelatin and whisk to combine. Remove from heat and place under a mixer. Set the mixer at slow speed. Gradually add the sugar-water mixture. Continue to mix at slow speed until the mixture has cooled. Then stir in the melted white chocolate. Fold a large spoonful of whipped cream into the chocolate mixture to lighten it, then fold the mixtures together, being careful to preserve volume. Fold in the remaining tablespoon of rum.

To assemble: Line a 10-inch round pan with plastic wrap. Slice the chocolate cake into 2 layers. Spread half of the ganache on one of the layers. Invert the layer into the prepared cake pan so that the ganache is on the bottom. Brush the cake with half of the syrup. Sprinkle with drained, rum-soaked raisins. Top with the white chocolate mousse. Place the second cake layer into the mold and brush with the remaining syrup. Spread ganache on top and refrigerate for at least 6 hours, or overnight.

To serve: Invert the pan onto a decorative cake plate and remove the cake pan. Cut into individual slices with a serrated knife, dipping the knife into hot water and wiping between each cut. Lightly dust the rims of the serving plates with cocoa powder. Place a cake slice on each. Drizzle the cake and serving plates with dark and white chocolate. If you will not be serving the entire cake, separate each cut with a piece of parchment paper, cover the top with parchment paper, and then invert the mold back over the cake before storing.