Rainbow Unicorn Cake

Rainbow Unicorn Cake

I got to make the *cutest* cake for a little 3-year-old! 

I got to make the cutest birthday cake a few months ago. To be honest, I debated whether or not to add this post to the blog. Mostly  because I think the video alone is probably more helpful than a printed recipe to anyone wanting to make a similar cake! 

That said though...I also realized that sometimes it helps to have the guesswork taken out of the cake/frosting recipes. I also realized it might be helpful to have supply links if you’ve never purchased fondant or gum paste before! (So both are below!)  Please send me an email if you have any questions or get into the recipe and hit any snags. All emails through my contact page go straight to my inbox! 

Recipe note - 

I made the decorations for this cake a couple days in advance. I wanted to make sure they'd set and wouldn’t ‘wilt’ on the cake. If you don’t have that much time ahead, I’d assemble at least the rainbow with a paper or cardboard backing so it doesn’t come apart on the cake while you decorate!

Recipe / video note - 

If you're watching the video closely, you'll see a raspberry and a blueberry cake layer. Per request, I modified my usual two-layer cake recipe, taking out the cocoa powder and adding raspberry and blueberry jams, and using buttermilk instead of regular milk. When I don’t have a specific flavor request though, below is the two-layer cake recipe I use! 

(Disclosure: As an Amazon associate I may earn from qualifying purchases, and my posts often contain affiliate links. If you click a link and make a purchase, I may receive a commission at no extra cost to you!) 

Rainbow Unicorn Cake

Rainbows and unicorns are both endlessly popular on their own, and this Rainbow Unicorn cake is just adorable and sure to please!
Prep Time30 minutes
Cook Time37 minutes
Decorating time1 hour
Course: Dessert
Cuisine: American
Keyword: First Birthday Unicorn Cake, Rainbow Birthday Cake, Rainbow Unicorn Cake, Unicorn Cake
Servings: 16 servings
Calories: 586kcal
Author: Sarah H


Cake layers

  • 1 ½ cups all purpose flour
  • 1 ½ cups sugar
  • 1 cup cocoa powder
  • ¾ teaspoon baking soda
  • ¾ teaspoon salt
  • ¾ cup unsalted butter, softened (1 ½ sticks; softened)
  • 3 large eggs (at room temperature)
  • 1 ¼ cup buttermilk
  • 2 teaspoons vanilla extract

Cream Cheese Buttercream Frosting

  • 6 ounces cream cheese (¾ package, softened)
  • ¾ cup butter (1 ½ sticks, softened)
  • 5 cups powdered sugar
  • 2-3 Tablespoons milk
  • 1 Tablespoon clear vanilla extract
  • 2-3 drops blue food coloring (Save and add later!)



Cake layers

  • Preheat an oven to 350 degrees F (180C). Prepare cake pans with baker's floured spray (or grease and line with parchment rounds).
  • Mix together dry ingredients (flour, sugar, cocoa powder, baking soda, and salt) in the bowl of a stand mixer with a paddle (or hand mixer or whisk) until well combined. Add in bits of softened butter, mixing until no lumps of butter are visible and the mixture looks crumbly.
  • Whisk together eggs, buttermilk, and vanilla. Add to dry ingredients and mix until no dry ingredients are visible. Scrape down the bowl and beat for another 20 seconds.
  • Fill the pans evenly - I find a kitchen scale helpful for this part, and each of mine weighed out to about 600g. Bake for 30-35 min or until a toothpick inserted comes out clean.
  • Cool 10-15 minutes before removing cakes from pans. Allow to cool completely before decorating – set in the fridge or freezer to accelerate the cooling process if desired. (This is a great time to make your frosting!)

Cream Cheese Buttercream Frosting

  • Beat together softened cream cheese and butter; slowly add in powdered sugar alternating with milk until frosting reaches desired consistency. Add vanilla (+ 1/4 teaspoon salt if using unsalted butter) and beat until well combined.
  • Remove about 1/2 cup of frosting (keep this white) and color the remaining frosting light blue.


  • Once your cake layers are cool, level them (if needed). This can be done with a cake leveler or a large serrated knife and a ruler. Place a smear of frosting on your cake circle (to keep the cake from sliding while you decorate it) and center your first cake layer in the center of the circle.
  • Spread the layer with frosting, and add your second cake layer on top. Now you're ready to crumb-coat . If you're unfamiliar with crumb-coating, it's just what it sounds like – spreading a thin layer of frosting over the entire outside of the cake to keep crumbs out of your final layer.
  • Once your crumb coat has set (this takes about 5-10 minutes in the fridge), add your final layer of frosting and smooth – I started with white, covering the cake top and about ½ inch down the side of the cake, and then covered the rest with light blue frosting. I like to use an offset spatula and bench scraper to smooth the icing on the cake.

Decorations - Unicorn

  • I’ll do my best to describe making the unicorn – since I forgot to film that step. :/ (Sorry!) Start with a pink fondant rectangle (for the body) and a slightly smaller square (for the head). Cut a small arc out of the rectangle to make the feet. Using a bit of water to adhere the pieces together, adhere a small flattened green ball to the top right side of the rectangle, then add the square to make the neck / head. Add a band of yellow at the feet, and a small white tail (see photo).
  • (The face details are fairly straightforward - the pieces are just a little fussy to work with since they’re so small.) I added a small half-circle to the lower portion of the face, and then very thin white and black circles to form the eyes. I cut a ‘v’ in a small red circle for the mouth, and actually used that piece to place the three dots for the nose and cheeks. Two small triangles and a tiny unicorn horn (optional) – and then leave it to dry and you’re done!

Decorations - Rainbow & Sun

  • The rainbow and sun are both shown in the video! For the rainbow, roll out progressively longer strips of each successive color of fondant (I used pink, then purple, blue, green, yellow, orange, and finally red). Adhere them together with a brush of water and leave the rainbow to set and dry. Lettering is optional, but here’s a letter-cutter set similar to mine!
  • I used a yellow small flattened circle and a long strip that I cut into triangles to form the sun – sticking a thin skewer into the base when I was done.

Decorating - Clouds

  • I used a clip-art paper template to cut out the clouds (google will pull up about a thousand shape options), and cut these out of gum paste. Once I left them to dry for about 24 hours they stayed up great even though I only used a tiny bit of icing to adhere them to the cake, cake top, and cake circle.
  • And you're done! Enjoy!



(Please note nutrition information is an estimate and may not be exactly accurate.) 


Serving: 1slice | Calories: 586kcal | Carbohydrates: 76g | Protein: 7g | Fat: 28g

Lol - one huuuge text box later - there are all my tips for this cake! Again; please send me an email if you have any questions or problems! 

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