When I was a kid we used to press flowers and leaves in books. Every once in a while I still find a fern or a daisy in an old book. You can get the same feeling without the mildew!
Did you ever make sunprints as a kid with that crazy probably super toxic blue paper? You lay something on top of it that you want a silhouette of and just leave it in the sun and you get something that looks almost exactly like this cake! This was done with food coloring in an airbrush gun and flowers as a stencil. Incredible effect, and you can eat it!