This is the recipe (or similar...with the cake mix) I use for my Giant Cookie. I just spread the entire mix out onto a cookie sheet and bake! Then, after it cools, I decorate it with Buttercream icing!
I made two of these for twins, but on these I used refrigerated chocolate chip cookie dough. I made Frozen Buttercream Transfers into Tinkerbell and Hello Kitty for these. THe girls loved them!
I used a white cake mix and added Andes Mints chips for a giant cookie once. I used a cheap, disposable cookie sheet I got at the Dollar Tree (in a two-pack), then just left pan and all at the party! I really liked this one's flavor!!!