I found a small sand castle form that I want to use to make a small cake with. It is plastic, so I can't bake the cake in it, but I'd love for the cake to have the shape of the form. Does anyone have any ideas of how to use the plastic form to create the cake in this shape? If I can't make it from cake, I'll do rice krispy treat, but I'd rather make it from cake. Thanks for any tips!