Triple Chocolate Truffle Cake
Preheat oven to 325 degrees. Arrange rack in center of oven. Butter the bottom and sides of a 9 by 2-inch round cake pan and line the bottom with parchment paper.
Melt butter and semi-sweet chocolate chips over double boiler until smooth; cool slightly. Meanwhile, with a hand mixer or in the bowl of an electric mixer fitted with the whip attachment, whip eggs and salt on medium speed until doubled in volume, about 5 minutes.
Gently fold, in thirds, whipped eggs into melted chocolate. Pour batter into prepared cake pan and place pan in water bath (see note below). Bake until the cake pulls away from the sides of the pan and is set in the center, about 40 minutes. Remove pan from water bath to a cooling rack and cool cake completely in pan. Cover with plastic wrap and refrigerate overnight. To remove cake, dip the bottom and halfway up the sides of the pan in warm water and run a thin metal spatula around the inside of the pan. Invert onto a plate to unmold, remove parchment paper.
To prepare ganache, bring heavy cream to a simmer and pour over milk chocolate chips. Stir gently until smooth; cool slightly. Pour ganache over top of cake and spread with an offset spatula to evenly cover. (There will be some ganache left over.) Chill cake until ganache sets, about 30 minutes. To garnish, grate white chocolate bar on top of cake. Makes 8 to 12 servings.
Water bath: Fill a shallow container with warm water and place the cake pan in it. The water should reach about an inch up the cake pan. The water bath gently cooks the cake.