Diane - from White Marsh, MD
You would need four 9 x 13 in. cakes to get the same size as a full sheet cake (two cakes equal a half-sheet cake). To avoid cracks where the cakes come together, make sure you have equally leveled each of the cake layers and that they are perfectly straight. If you are stacking two or more layers, using dowel rods in the layers will assure they don’t shift, which can cause the cracked look in your icing. Once all the layers are in place, ice as you would a full sheet cake. You may need a bit more icing in the areas where the cakes meet, but it shouldn’t be evident in the final decorated cake!