How to make a Rainbow Swirl Cake
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!
In all of the cakes and cupcakes that we have on the blog, I have yet to add a rainbow cake…until now! This has always been on my baking wishlist, as I love playing with all of the colors. It’s such a fun and beautiful cake, and today, we’re walking you through how to make it even easier.
That means less bowls, less mess, but still the most beautiful rainbow swirl cake that’s fit for any St. Patrick’s Day celebration, Easter, graduation, birthday, or more!
How to make a rainbow swirl cake
For the base of this cake, we’re using my classic vegan vanilla cake. If you’ve found this recipe and this is your first time visiting The Banana Diaries- don’t worry! Our goal is to make eggless and dairy free treats taste just like the classic, and this vanilla cake in particular has been approved by all eaters, vegan or not.
In fact, my family, who are not vegan, requests it every time anyone has a birthday…that or my vegan chocolate cake!
This time, I’ve included the full written instructions down below in the recipe card, along with measurements in both the metric system and the US standard. This is to ensure that everyone will be able to make this cake (I’ve made this cake several times without weighing it- as long as you follow proper baking techniques, then you can achieve the same results!).
You’ll only need a few simple ingredients to make this vegan rainbow cake: flour, sugar, vegan butter (I like Flora Plant Butter, as it’s nut free and soy free), vegan buttermilk (a combination of dairy free milk and apple cider vinegar or lemon juice), applesauce, vanilla extract, and baking powder/soda. That’s really and truly it! Oh, and the vegan food coloring.
The rest of the baking process is very similar to how you would bake a regular cake. You can use a stand mixer or mix by hand. I’ve baked for years without a stand mixer, and only recently started using one. Sometimes, I prefer the hand mixer!
The trick to this cake really comes in with the rainbow swirl technique, which is much easier than other rainbow cakes. We’ll go over that now
The easiest rainbow swirl cake technique
So unlike other rainbow swirl cakes, I really didn’t want to have to go through six bowls to mix batter, when I was already going to use six bowls for mixing the frosting. I thought that there had to be an easier way to do this.
And there was.
Instead of doing a rainbow swirl cake that is a full rainbow, I decided let’s make an actual swirl. Some of the vanilla cake batter can still show, which will represent the yellow, but the others colors we’ll gently fold in, much like you’re swirling peanut butter into a peanut butter swirl brownie.
This method is actually so easy, and so much less work. I’m not one to want to spend hours cleaning dishes after I just spent hours building a cake.
To swirl the colors into the cake batter without over mixing, we’ll divide the cake batter evenly into the pans. Then add in your drops of vegan food coloring. I use the brand, Nomeca.
Use a butter knife and gently fold the vanilla batter over and under, swirling the colors into the cake. Be careful not to over mix the colors, as then you’ll muddy them.
Once you’ve swirled the colors, you’ll bake the cake according to the baking times below in the recipe card.
Rainbow cake decorating ideas
Once your cakes have baked and cooled, it’s time to decorate! This is my absolute favorite part. I’ve been posting quite a few cake decorating videos on Instagram and TikTok, so if this interests you, definitely go check them out!
The piping of the rainbow and its decorations is quite fun. The rainbow is very simple. You’ll need 6 pipings bags, one for each color. You can mark guidelines onto your cake to help make sure that your rainbow is even or you can do it free hand.
Once you’ve piping your rainbow, it’s time to decorate. If you want to do the multi-color swirl, like I did, simply lay out a piece of plastic wrap on the counter. Pipe in strips each color next to each other. Then carefully roll the plastic wrap lengthwise until it’s a cylinder. Cut the end of the plastic wrap and place it into a large piping bag with a piping tip. Then pipe the frosting onto your cake!
I hope you love this rainbow swirl cake as much as I do! If you try it out, let me know how it goes by leaving a comment down below, as well as a rating ⭐️⭐️⭐️⭐️⭐️ so that others may find this recipe!
As always, I absolutely love to see your beautiful creations on Instagram and Pinterest, so be sure to tag me there.
Happy rainbow cake baking!
More cake recipes you’ll love:
Best Vegan White Chocolate Cake
Want to save this recipe for later? Add it to your favorite recipe board on Pinterest!
Easy Rainbow Swirl Cake
- Prep Time: 20
- Cook Time: 30
- Total Time: 50 minutes
- Yield: 16 1x
- Category: Dessert
- Method: Baking
- Cuisine: American
- Diet: Vegan
Description
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!
Ingredients
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 1/2 batches vegan buttercream frosting
- Vegan food coloring (see Notes)
Instructions
- Preheat the oven to 350F and grease and line three 6″ cake pans with parchment paper. Set aside.
- 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.
- 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.
- Pour in the vegan butter milk, and beat again until the dry ingredients are completely incorporated into the batter.
- 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.
- 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.
- 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.
- 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.
- 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.
- Serve and enjoy!
Notes
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.
