White Chocolate Poinsettia Cake

Prepare the Cake Layers: Place white chocolate in a bowl. Pour boiling water over chocolate, and let stand 1 minute; stir until chocolate is melted and smooth. Cool completely.

Preheat oven to 350°F. Beat granulated sugar and butter with a heavy-duty stand mixer on medium speed until fluffy, about 5 minutes. Gradually add egg whites, a third at a time, beating well after each addition.

Sift together flour, baking powder, and salt; add to butter mixture alternately with white chocolate mixture, beginning and ending with flour mixture. Beat on low speed until blended after each addition. Add vanilla bean paste. Pour into 3 greased (with shortening) and floured 9-inch round cake pans.

Bake in preheated oven until a wooden pick inserted in center comes out clean, 22 to 25 minutes. Cool in pans on wire racks 10 minutes; remove from pans to wire racks, and cool completely.

Prepare the Mousse Filling: Microwave white chocolate chips and 1/4 cup of the cream in a microwave-safe glass bowl on MEDIUM (50% power) until melted and smooth, 1 1/2 to 2 minutes, stirring every 30 seconds. Stir in crème de cacao. Cool 5 minutes.

Beat remaining 1 cup cream with an electric mixer on medium speed until soft peaks form; fold into white chocolate mixture. Chill in refrigerator.

Prepare the Frosting: Microwave chopped chocolate and 1/3 cup heavy cream in a microwave-safe bowl on MEDIUM (50% power) until melted and smooth, 1 to 1 1/2 minutes, stirring every 30 seconds. (Do not overheat.) Cool completely.

Beat butter with an electric mixer on medium speed until creamy; gradually add powdered sugar, beating on low speed until blended after each addition. Add 1/4 cup heavy cream, 1 tablespoon at a time, beating on low until blended after each addition. Add salt and white chocolate mixture, and beat on low until combined; increase speed to high, and beat until light and fluffy. Stir in vanilla.

Assemble the Cake: Place 1 Cake Layer on a serving plate. Pipe a 1/2-inch-thick ring of Frosting around edge of Cake Layer. Spread half of Mousse Filling inside Frosting border; top with 1 Cake Layer. Pipe a 1/2-inch ring of Frosting around edge of Cake Layer. Spread remaining Filling inside border. Place remaining Cake Layer on top; spread top and sides of cake with remaining Frosting.