Don't be tempted to substitute peppermint extract for the peppermint oil used in this recipe. Peppermint oil, available from cake-supply stores, has an intense, highly concentrated flavor like that found in chocolate-covered peppermint patties.
Spoon batter evenly into 2 greased and floured 10-inch round cakepans. Bake at 350° for 30 minutes or until a wooden pick inserted in center of cake comes out clean. Cool in pans on a wire rack 10 minutes; remove from pans, and let cool completely on wire rack.
Stir together Vanilla Buttercream Frosting and peppermint oil until well blended. Spread frosting mixture evenly between cake layers. Spread Chocolate Ganache evenly over top and sides of cake.