If necessary, using serrated knife, cut rounded top off cakes to make a level surface. Place 1 cake layer on cake plate, top side up. Spread frosting over top. Top with another cake layer, top side down; spread with frosting. Top with remaining cake layer, top side down. Reserve about 1/2 cup remaining frosting for garnish. Frost side and top of cake with remaining frosting. Use metal spatula to smooth frosting. Using #9 writing tip, pipe reserved 1/2 cup frosting around bottom of cake.