Always use the pan size specified in a recipe. A pan too large will result in a thin, dry cake. A pan too small will not be large enough to hold the batter as it expands during baking and the cake will overflow in the oven. To substitute a different pan, check to make sure it holds the same volume as the pan called for in the recipe. For example, in this recipe an 8-inch square baking pan may be substituted for the 9-inch round baking pan.