How to make a cake for rabbits to eat?

my rabbits bitrthday is today and i need some ideas on how to make him a cake hopefully out of treats, oats, and or pellets. i really want him to be happy so please give me some really good ideas. and make shure they wont make him sick or die. he is now 2 years old and i want this birthday to be extra special. :) :) :)