I have a great recipe for a layer cake that bakes in 9-inch round pans, but I want to make a big sheet cake. Do I double the recipe, and double the frosting, and how long does it need to bake?
A 13 x 9-inch baking ban is just about equal to two 9-inch round cake pans in volume, so the amount of batter should be about right for a sheet cake pan. If you double your recipe you will have enough batter for two 13 x 9-inch sheet cakes.
The depth of both size pans is about the same (2 inches) so the baking times will be fairly similar. But, warns Michelle Tampakis, Senior Baking Instructor at the Institute of Culinary Education, be sure to test the cake with a wooden pick or cake tester and not judge doneness by time or color alone. The baking time could be a couple of minutes different, so test the cake on the early side of when you expect it to be done.
Just as the volume doubles from one 9-inch round cake pan to sheet cake pan, so does the surface area, which means that if you make two sheet cake layers, you may need to double the amount of frosting and/or filling. The frosting amounts used in different cakes will vary depending on whether you frost and/or fill between the cake layers, cover the whole cake or only the top with frosting, and how thick of a layer of frosting you like. You'll need between 2 to 4 cups of frosting to cover a one-layer 13 x 9-inch sheet cake.