Here is a cake I made for my 21st birthday. It has a surprise inside!
I piped the rose crest from Revolutionary Girl Utena onto an oreo-buttercream-frosted cake, then filled in the "stained glass" with sugar sprinkles.
And when you cut into it - it's a rainbow inside! 3 layers of cake (blue, yellow and red) - with green frosting and orange frosting to finish off the gaps in the rainbow. Next time I try something like this, I think I will use bolder food coloring in the cake mix. This one was rather pastel (which was also cute).