I started with Bob's Red Mill Gluten Free Chocolate Cake Mix. I mixed it together according to the directions on the package, but I added about 1/2 cup cornstarch to the dry ingredients (Sarah figured out that cornstarch really improves the texture of a baked item). I put it in a 9x13 glass pan, though the package recommends to 8" round cake pans, and sprinkled chopped walnuts, Hershey's chocolate chips and Kraft Miniature marshmallows on top. I then baked it for the amount of time the package suggested for the 8" cakes.
This cake had a great texture and was delicious. It was smooth and the flavor was very much like a Devil's Food cake. It was for my mother's birthday and she said it was the best chocolate cake she had ever eaten. Did I mention she isn't gluten intolerant?