Our tall cake gets its extra height from stacking two wedding-cake tiers of the same diameter (10 inches). The stacked tiers are then covered in a single layer of fondant. Each tier itself has five layers of red-velvet cake interspersed with white buttercream. Since the layers are created by splitting a basic cake horizontally into three layers, you'll need to make this batter recipe twice. See the assembly instructions at the end of the recipe.