You can freeze the cake layers and cookies weeks ahead, then assemble the cake (except adding the angel cookies) a day or two before your party. Add the cookies and ribbon up to 6 hours before serving. If you like making the chocolate-praline truffles, try these truffle recipes for more festive and rich desserts.
Prepare Chocolate Cake batter, and pour into 3 greased and floured 8-inch round cakepans.
Bake at 350° for 18 to 20 minutes or until a wooden pick inserted in center comes out clean. Cool in pans on wire racks 10 minutes; remove from pans, and cool completely on wire racks.
Prepare mixture for Chocolate-Praline Truffles, and spread a thin layer between cake layers and on top and sides of cake. Cover and chill at least 2 hours.
Reserve 1 1/2 cups White Chocolate Buttercream Frosting. Spread remaining frosting on top and sides of cake.
Spoon reserved frosting into a heavy-duty zip-top plastic bag; seal bag, and snip a 1/4-inch hole in 1 corner of bag. Pipe frosting around base of cake, creating a ruffle. Pipe about 1 teaspoon frosting on back of each Angel Shortbread Cookie. Press cookies against sides of cake, spacing evenly. (Wingtips should be about1/2 inch apart.)
Cut ribbon into 6 (4-inch) lengths; crumple slightly. Place each piece loosely against side of cake between each pair of angel cookies, inserting ends under angel waists. Sprinkle shaved white chocolate on top of cake. Store in refrigerator up to 2 days without cookies, up to 6 hours with cookies (which will soften if chilled longer). Remove up to 2 hours before serving; serve at room temperature.