Grease and flour an 8x8x2-inch baking pan; set aside. In a heavy saucepan place chopped unsweetened chocolate over low heat, stirring constantly, until chocolate just starts to melt. Remove from heat. Stir until smooth; cool. Stir together the flour, baking powder, baking soda, and salt; set aside.

In a large mixing bowl beat the butter with an electric mixer on medium to high speed for 30 seconds. Add sugar; beat until well combined. Add eggs, 1 at a time, beating well after each. Beat in chocolate and the 2 tablespoons liqueur. Add flour mixture and water alternately to egg mixture, beating on low speed after each addition just until combined. Stir in orange peel. Pour batter into the prepared pan.

Bake in a 350 degree F oven about 35 minutes or until a wooden toothpick inserted near the center comes out clean. Cool cake on a wire rack for 10 minutes. Loosen edges of cake with a spatula. Invert onto a wire rack. Remove the pan. Cool cake thoroughly on wire rack.

Combine the 1 tablespoon liqueur and orange juice. Split cake in half horizontally. Sprinkle each cut side with half of the liqueur mixture. Place bottom half of cake, cut side up. on a platter; spread the marmalade evenly on top. Top with remaining cake layers, cut side down.

Frost the cake with Bittersweet Chocolate Icing. (You can frost the cake several hours before serving.) If desired, decorate the sides of the frosted cake with chocolate curls pressed into icing. Makes 10 servings.

In a heavy small saucepan combine 1/3 cup whipping cream and 1 tablespoon light-colored corn syrup. Bring just to boiling, stirring constantly. Remove from heat. Stir in 6 ounces semisweet chocolate, finely chopped, or 1 cup semisweet chocolate pieces, stirring until chocolate is melted and mixture is smooth. Cool to room temperature. Stir before using. Makes 1-1/4 cups (8 to 10 servings).

Prepare as above, except substitute raspberry liqueur for the orange liqueur and seedless raspberry preserves for the orange marmalade.

Chocolate curls -- whether used as a smattering on top of a cream pie or as a border around a cake -- make exquisite dessert decorations. To make curls, carefully draw a vegetable peeler across a bar of chocolate (milk chocolate works best). For narrow curls, use the short side of the bar; for wide curls, use the broad surface.