First bake your favorite cake in a 13 x 9 pan. Let cool. After about 20 min. of cooling time you can put it in the freezer, so it will be easier to carve. Meanwhile draw a template of the shape of the speak and spell onto a paper or card board I like to use empty cereal boxes. Then cut it out. This is just a guide when it comes down to it, you will eyeball it and make sure it looks nice. Take the cake out of freezer and use a serrated knife to “trace” your cake. Once you have the basic shape you can start making sure that it has straight edges where it needs straight edges and well, you get the idea, just clean it up a bit. Always remember… you can always take a little cake off but it’s hard to put it back on so just trim a little bit at a time.
When you are happy with the shape, let the cake chill for a while, then take out and cover with icing.