This recipe as is makes an 8"x8" cake. I'm sure you could use a 9"x9" pan if desired, but you will likely need to reduce the baking time a bit. If you'd like to make an 9"x13" cake, I'd recommend increasing the recipe by 1.5 or doubling the recipe. You will have to adjust the baking time accordingly. The cake is done when a toothpick inserted in the center comes out clean, or with a few moist crumbs, but no wet batter.