My son loves the Captain Underpants books by Dav Pilkey and that was all he wanted for his 7th birthday cake.
This Captain Underpants Cake is two square cakes glued together with icing. The cake is decorated with standard butter icing and (except for the character) just piped onto the cake.
For Captain Underpants, I got a cartoon picture of Captain Underpants and enlarged it to the size I needed for the cake. I’m not very good at freehand drawing, so I cut the picture into sections and iced each section in its appropriate colour (like a reverse jigsaw), removing each section as it had been iced, so that in the end the whole picture was iced in.
Then I got strip licorice pieces, cut it super thin and used that to define the different sections so the picture showed up more. Sounds a bit complicated, but it’s really easy and if you have a good look at the cake photo, you’ll see how I did it. Was a great, easy project and all the kids at my son’s party thought it was brilliant.