How to Make It
Preheat oven to 350°F. Beat butter at medium speed with a heavy-duty stand mixer until creamy; gradually add sugar, and beat until light and fluffy, about 3 to 4 minutes.
Sift together cake flour, baking powder, and salt; gradually add to butter mixture alternately with Champagne, beginning and ending with flour mixture, beating just until blended after each addition. Stir in vanilla.
Beat egg whites with an electric mixer at medium-high speed until stiff peaks form. Fold one-third of egg whites into batter; fold remaining egg whites into batter. Pour batter evenly into 4 greased (with shortening) and floured 8-inch round cake pans.
Bake in preheated oven until a wooden pick inserted in center comes out clean, 17 to 19 minutes. Cool in pans on wire racks 10 minutes; remove from pans to wire racks, and cool completely, about 30 minutes.
Reserve 1 cup of Champagne Buttercream, if desired, to pipe decorative stars. Spread Champagne Buttercream between layers, and on top and sides of cake.
Roll fondant (about 2 oz.) to 1/8-inch thickness. Use cookie cutters to cut out numbers. Place cut out numbers on a paper towel or piece of parchment paper. Spray numbers with edible gold color spray. Allow to dry completely, about 4 hours. Using a small paint brush, brush dried numbers with edible gold luster dust. Garnish with fondant numbers, and pipe top of cake, using a 2D star tip, with stars, if desired.