My son & I made our first rainbow cake this week-end! I've been waiting for a chance to try this and finally had the perfect opportunity for my cousin's birthday. I love that it looks like a regular cake from the outside and then you get to see everyone's surprise when you cut out the first piece. Our boys thought it was really cool and "the best cake ever".
If you google "rainbow cake" you will find a million versions and recipes. I took the easy route and bought a mix. It's as simple as:
1) Mix your batter according to packaging or recipe.
2) Separate the batter into 6 equal portions & color each portion separately (use
food colouring gel if you want the color to come out vibrant).
3) Cook each portion separately (I did two portions at a time for 10 minutes each - use a toothpick in the center of the cake to make sure it's well baked. If the toothpick comes out clean it's ready).
4) Let cool a few minutes then turn out on a cooling rack and let cool completely.
5) Ice between each layer, on top and all around.
If your layers don't bake flat you can either trim the top off each layer or keep them as is but then you may need to place a couple wood skewers (I used plastic straws) near the center of the cake to keep it from sliding to one side.
I used edible paper to cut out hearts to decorate the top. It can be found
here.