Omnomicon's blog. I am not sure why - but I needed to make this cake.
Mother's Day brunch for our families (I wasn't a mother at the time). It's a great cake for a kid's birthday party or a party with an art or rainbow theme. Omnomicon uses a diet cake recipe to make her cake, but I try not to make anything "diet" for company unless I've tried it before. I ended up using two boxes of Betty Crocker French Vanilla cake. In order to avoid having to wash 6 extra dishes I opted to dye the cake mix in 6 plastic cups. This made for an easy cleanup - and it also made the transfer to the pan easier (I just poured the batter straight from the cup). I wasn't sure how difficult it would be to layer the colors, but it turned out to be quite simple. As you add a new color to the center of the pan, the rings push themselves outward. I did the rainbow (with pink instead of red), but you could do this with any color combination.
I may have had a little to much fun making this cake, and it was very well received.
I thought about dying the frosting blue (like a sky) and adding marzipan white clouds on the cake - for the whole sky/rainbow effect, but I figured there was enough food coloring in the cake, so I ended up going with white frosting. In the end I was happy with the white frosting as it added to the surprise. It was deceivingly boring from the outside - and it was initially "rejected" when my nieces and nephew pointed to the desserts they wanted to try.
I would highly recommend checking it out the step by step "How to Make" on Omnomicon's blog for the full details.