This Sonic birthday cake was harder than I anticipated but it turned out OK. I was not happy with it but the birthday girl loved it!
I baked a cake in a 10in and an 8in round pan, more in the 10in. I drew out the picture on the 10in first and started carving away. When I had the bottom part done, I put the 8in on top and carved that.
I covered the entire thing in butter cream frosting, followed by a layer of white marshmallow fondant. Then I proceeded to cover the rest of the cake in the appropriate colors and used a skewer stick to shape it into the corners.