Tutorial: Rainbow Cake The “Easy Cheater” Way

I first saw a Rainbow cake in all it’s splendor in this amazing post by Whisk Kid. This cake was so spectacular that it ended up on the Martha Stewart Show. Awe inspiring. As is Whisk Kid herself.


I’m pretty sure that one of the requirements for appearing on Martha Stewart is that you must make things that intimidate the other busy mortals a bit, ie: preparing an elaborate make-you-or-break-you frosting that requires whisking egg whites and sugar together on the hot stove (without cooking).

It’s not that I couldn’t do this. I’m sure it’s loads of fun and totally possible for less distracted mortals. I however have four young kids that could never appreciate this level of cake dedication nearly enough.

In fact, they might learn curse words from me as I neglected them to attend to the frosting and what a sweet story that would make for the child protective services agents who popped over to see why my kids were roaming the streets swearing like sailors while I perfected meringue frosting.

This much I know about my children’s birthday parties:

  • Birthday treats are not the cause of obesity. Every day treats and unhealthy diets are. If you are gonna have cake, make it  rare and special and a real treat.
  • But… no matter how special, half of the special cake will probably end up on the floor, and in the trash when kids take a bite and run off to play*. That’s ok.
  • Frosting will be smeared on my butt and hip after my toddler forgoes the napkin and wipes his face and hands on me.
  • The only person who will actually taste and judge my cake’s quality will be the alarmingly skinny mom of my child’s meanest classmate who will eat one bite of her child’s serving of cake, quiz me about ingredients, pass judgment on whether it is “good” enough for her offspring and then declare it unfit for her herself and her lo carb lifestyle no matter how delicious. I’m so not baking for her.

My family is precious, for certain. But so is my time and sanity. So in an homage to the original, I’ve dumbed this down for the time-crunched masses who want a tasty, doable cake that looks DAMN good. There’s a brief nod & some ingredient tweaks for those (ok, yeah, me) who despite being time crunches, have issues with boxed mix and canned frosting. But not nearly enough tweaks for the judgy low carb mom. She won’t approve of the sugar, fat, food coloring or basically anything in this cake. Trust me. She wouldn’t approve even if you did make meringue icing.

* The child of judgy mom will be the exception to the above rule and will eat every morsel of cake on their plate. And possibly half of someone else’s abandoned piece. Don’t give them too big of a slice. They aren’t used to the carbs and may get ill.

Now that we’re clear.

When it came time to  assemble this cake I received extra coaching from Angry Julie Monday & her pal S. (aka best friend ever). Julie has a great rainbow cake assembly photo tutorial on her site. I also got the boxed mix “doctoring” recipe (which I doctored some more) from Angry Julie. Worked like a charm to make box mix cake taste like good bakery cake.

Prepare the Cake

  1. Start with two boxes of white cake mix. White is best for keeping color vibrant. Doctor the mix with these instructions. I also added the zest of one lemon to the mix (half a lemon per box).
  2. Divide batter into six bowls and color each using gel colors. I used Duff’s which I bought at Michael’s. It’s nice because it’s squeezable. Note: When making Orange, start with yellow and add red slowly. When making purple, start with red and add blue sparingly. It works better in that order.
  3. Pour each color of batter into a separate 9 inch pan and bake according to package directions. You can do them two or three at a time if you have enough pans. Angry Julie’s pal S. suggested using Pam spray for baking (contains flour) for the pans and it did seem to work like a charm. Nothing stuck.
  4. Cool the cakes completely.
  5. Now you must be ruthless. If you hate to waste food it may be tough to do this but brace yourself. You must slice off the top of each cake so that it is as totally flat/even as possible and the layer is not too thick. Use a long serrated knife and be careful! Best to work on the highest counter you have so you can lean over and “eyeball” the layer for level-ness.

Make The Frosting

Buttercream and me don’t get along. I have yet to find a recipe that consistently yields the right consistency. I don’t have time to make mistakes. So… I’m looking at the canned stuff next to the boxed cake mixes.

Do you like canned frosting? I don’t! It makes my eyes water it is so sweet. I am a little appalled by the unnaturalness of it too. It’s not that I am such a snob. It just tastes awful to me.  Until I cut it with cream cheese. Cream cheese makes everything better. Stick to the classic full fat brick and it’s pretty much impossible to mess up when you try this “recipe”.

You can go as high as 50/50 cream cheese/frosting. I do about 2 parts frosting to 1 part cream cheese for a kid’s cake.  I also like to add a little (tsp) of good vanilla to the white frosting for flavor.

For this ginormous cake I whipped up two bricks of cream cheese and 3 cans of white frosting in my trusty pink Kitchenaid mixer and had a fair amount left over. It was a LOT of frosting.

After you make the frosting, stick in the freezer for 15 minutes to set, or chill for up to a day.

No it’s not lemon merinque buttercream, but please remember it is ending up on my bum. Even if I don’t partake.

Assemble The Cake

Note: For a classic cake remember your rainbow color order…. ROY G BIV. Red Orange Yellow Green Blue Indigo (but we scratched Indigo) Violet.

  1. Starting in reverse order (with violet on the bottom) I laid down a layer of cake, slopped on about a half to three quarter cup glop of frosting in the center of the layer, spread out with a frosting spreader and then slapped on the next layer of cake.
  2. Slop, slap repeat to construct. But do so CAREFULLY and GENTLY. Don’t literally slap, ok? Keep frosting cold so it stays semi firm and “sticky”, but still spreadable.
  3. This cake, by the time you get to the red layer, is super tall. To keep it from toppling, we used the  3-4 plastic straws in lieu of skewers or whatever it is you normally use to hold your cake together. Do this after you’ve placed the final layer on top. Just shove the straws right on down into the cake. The straws are easy to trim to height and do the trick quite well.
  4. Chill your stacked cake for a bit (about 15 min in freezer) and have a cup of coffee to celebrate having done the hard part.

The rest as they say, is frosting. A whole lot of frosting. I recommend doing in two batches. A thin coat to set the crumbs, followed by another chill session and a second thicker coat. But you can do it all at once if you lack the patience and time to frost twice. Keep the cake cold and allow to come to room temp before serving. Store leftovers in the fridge!

Is this cake a fair amouunt of work? Yes. But given the box mix and doctored frosting tricks, it’s something that pretty much anyone can do, and the “wow” factor is priceless when you cut it open. People will whip out their cell phones to take pics.

Feel free to tell judgy mom you made it from scratch. I won’t tell on you.


  1. lisa says

    Your cake is great and so’s your attitude. If you were my neighbor i’d invite you over to my messy house, batter smeared butt and all. : )

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