How do I make a cake that has to do with the 5 layers of the epidermis?
Use different layers with different colors and fillings to represent the structure and cell types in each layer.
Fun project! You can use a basic white cake and add coloring to make pink or green or blue layers. Use chocolate cake for brown textures. You can add edible things like licorice strips, raisins, M&Ms, chocolate chips, Gummi Bears, candy corn or whatever works to make things like hair follicles and sweat glands or other larger sub-structures in the skin.
The trick is to bake each layer separately - they should only be about 1/2-3/4" thick, so they will bake faster than a 'standard' cake. When the layers are baked, assemble them into one cake, which now can be peeled back or cut across to show graphically (and edibly!) the structure of the epidermis.