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slice of rainbow cake

Easy Rainbow Swirl Cake

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  • Author: thebananadiaries
  • Prep Time: 20
  • Cook Time: 30
  • Total Time: 50 minutes
  • Yield: 16 1x
  • Category: Dessert
  • Method: Baking
  • Cuisine: American
  • Diet: Vegan


Learn how to make the easiest rainbow swirl cake that looks incredible but takes much less effort! Using our favorite secretly vegan vanilla cake and natural food colors, this rainbow swirl cake is the perfect celebration cake for St. Patrick’s Day, Easter, Spring, birthdays, and more!



Vanilla Rainbow Cake:

  •  3 1/2 cups (438 grams) cake flour
  • 2 1/2 tsp baking powder
  • 1/2 tsp baking soda
  • 1/2 tsp granulated sea salt
  • 1 1/2 cups (300 grams) granulated sugar 
  • 1 1/2 cups (321 grams) dairy free milk, room temperature
  • 1 tsp apple cider vinegar
  • 3/4 cup (188 grams) unsweetened applesauce, room temperature
  • 1/3 cup (76 grams) vegan butter, room temperature
  • 2 tbsp vanilla extract

Vegan buttercream frosting with Rainbow:


  1. Preheat the oven to 350F and grease and line three 6″ cake pans with parchment paper. Set aside.
  2. Make the cake: In a medium bowl, whisk together the flour, baking powder, baking soda, and sea salt. In a separate small bowl, combine the dairy free milk with the apple cider vinegar and mix together. Set aside for 5 minutes to curdle and become the vegan buttermilk.
  3. In a large bowl or a stand mixer, cream together the vegan butter and sugar until light and fluffy, about 2-3 minutes, scraping down the sides as needed. Add in the applesauce and vanilla extract, and mix again on high speed until combined. Make sure to scrape down the sides as needed, as well as the bottom of the bowl to ensure everything is mixed. The mixture will appear soupy. Add in the dry ingredients and mix on medium low speed until just combined. 
  4. Pour in the vegan butter milk, and beat again until the dry ingredients are completely incorporated into the batter. 
  5. Divide the batter evenly among the cake pans. Add a few drops of vegan food coloring to each cake pan. I did red, orange, green, blue, and purple each in each cake pan. Use a rubber spatula and gently fold the batter to distribute the color, being careful not to over mix. You just want swirls of color, much like swirling peanut butter onto peanut butter swirl brownies.
  6. Place the cake pans into the oven to bake for 27-30 minutes, or until the toothpick comes out clean. Remove from the oven, and allow the cakes to fully cool before frosting. They need to be entirely cool and have absolutely no warmth to the touch on either side of the cakes before frosting.
  7. Make vegan buttercream: prepare the vegan buttercream according to the instructions in the post linked in the ingredients section. Reserve about 1/3 of the frosting for the rainbow and piping. Divide that reserved frosting into 6 bowls. Add 2-3 drops of each vegan food color (red, orange, yellow, green, blue, purple) into their respective bowls (one for red, one for orange, and so on). Mix the food coloring until the frosting is saturated. Set aside.
  8. Assemble the cake: frost and assemble your layer cake. A cake turntable is helpful here, along with a bench scraper and offset spatula. I use about 1/3 cup frosting in the middle of each cake. Spread the frosting to the edges and top with the second layer. Repeat and top with the third layer. Then frost the outside of the cake, creating a crumb coat. Chill the cake for 20 minutes (and chill your frostings too, including the rainbow colors, if needed). Remove from the fridge and frost with the remaining white buttercream frosting. 
  9. Piping the rainbow: Fill each color frosting into its own piping bag. Pipe the rainbow onto the side of the cake, going from red, orange, yellow, green, blue, and purple. Any remaining frosting, you can place into an extra large piping bag with a fitted piping tip. Pipe your desired design onto the top and bottom of the cake.
  10. Serve and enjoy!


Vegan food coloring: I recommend Nomeca, but Whole Foods 365 brand also works well. Some Wilton food colors are vegan, but you need to check the labels. You can also use powdered food coloring, such as Suncore Foods.