Rainbow Birthday Cake


I need to take a break from our Harvest theme to tell you about Ana’s Rainbow Birthday Cake (but don’t forget to enter our latest giveaway!)

My niece, Anastasia, recently turned 6. When I asked her what kind of cake she would like to do for her special day, she looked at me in confusion. She truly didn’t know where to start. However, with very little prompting at all, she began, “I want a square cake…with a heart on it…and a number 6 candle on top…and I want it to be rainbow”. Wow! She really got specific, right? So, I got started. I googled images for “rainbow birthday cake”. There were cakes in the shape of a rainbow, frosted in rainbow colors, swirled colored cake in rainbow patterns, and then there was this idea (originally from Whisk Kid – a super-sassy baking blog that I <3).

It was PERFECT! I couldn’t wait to get started. I have to be honest, though, I did have some anxiety about pulling this off. But it couldn’t have been easier (especially since I cheated and used a white cake mix). I used three, square pans (she wanted square, right?!) and baked one layer of each color. Check out amazon.com to buy Wilton Gel Food Colors.

Once the layers were cooled, all I had to do was stack and frost to hide the rainbow. I did use the Lemony Swiss Meringue Buttercream recipe and it is to die for! I topped the cake with a heart and a number 6 candle and went to get Ana from school.

Ana walked up to the dining room table where the cake was waiting for her. She crawled up on the chair to take inventory of her very own creation. “It’s a square! And there’s a heart, and a number 6 candle!” Then, very quietly, she said, “but where’s the rainbow?” Well, we had to go to dinner and gymnastics class, so that surprise waited until we got home. When she finally got to cut into that cake, the smile on her face was the greatest reward for me. “There’s the rainbow!” she laughed.

So, Ana got all of her birthday wishes fulfilled, and Auntie Joy was a baking hero.

Who is your hometown culinary hero? Enter here to win our latest giveaway.

Rainbow Birthday Cake
Recipe Type: Dessert
Author: Frosting by Whisk Kid
Serves: 12
Be sure to line the pans with parchment paper for easy removal. Gel food colors are available at Amazon.
  • 2 boxes of white cake mix (prepared according to directions)
  • Gel food colors: red, orange, yellow, green, blue, violet
  • Frosting to fill and crumb coat:
  • 9 egg whites
  • 1 ” c (350 g) sugar
  • 4 sticks (532 g) of butter, room temp
  • 2 tsp lemon extract
  • To frost:
  • 5 egg whites
  • 1 c (200 g) sugar
  • 2 sticks (226 g) butter, room temp
  • 1 tsp lemon extract
  1. Preheat the oven to 350°, or according to directions on the box.
  2. Oil your cake pans and line them with parchment paper. Oil, again.
  3. Prepare the cake according to the directions on the box.
  4. Divide the batter into six bowls and add color to each one (it will be the same color when it’s baked).
  5. Pour the batter into separate pans and bake.
  6. Let cool for about 5 minutes before removing the paper-lined cake to a cooling rack. Slowly and carefully remove the paper.
  7. To make the frosting:
  8. Cook the egg whites and sugar in a small saucepan over medium heat, whisking constantly, until the sugar is completely dissolved (test by rubbing some between your fingers. If it’s completely smooth, it’s done).
  9. Pour into another bowl (a stand mixer is preferable) and whip on high speed until room temp.
  10. Then, on a medium-slow speed, add the butter, waiting until each piece is completely incorporated before adding the next.
  11. After all the butter has been added, turn the mixer back to high speed and whip until it has come together, about five minutes.
  12. Add the extract, beat briefly and then use.
  13. If the buttercream seems soupy after all of the butter is added and does not come together after whipping, refrigerate for 5 to 7 minutes and continue whipping until it becomes fluffy and workable.
  14. Assemble: Stack the layers in your preferred order and fill and frost as you would any other cake.


  1. Jim says:

    Joy, the cake looks very interesting (and maybe a lot of work–but worth it for the big smiles). Your niece is very cute, and you’re right: the smile makes it all worthwhile.

    Jim Oswald

    • JoyAldrich says:

      Thanks, Jim! One thing I forgot to mention is that it really tasted good, too. So many fancy cakes lack flavor, but this was really delicious.

  2. farida says:

    So pretty cake and interesting to make it soon, thanks for share

  3. Mo Johnson says:

    I love it Joy! Those pictures and cake just make me smile!

  4. Marie McFadden says:

    The cake turned out fantastic and she is adorable!

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