Way Beyond Cakes by Mayen: Build Your Cake Upside Down Method - making a double barrel cake ( using swiss meringue buttercream ) 1. Get a big sheet of parchment - much bigger than the size of your cake. Lay it on a big flat turntable surface . Put a layer of buttercream on it - if your cake is 8 inches, make a 9 inch round layer of BC (buttercream) . 2. This cake has 2 cake layers on the top half and 2 cake layers on the bottom . . .