Let’s bake and decorate these vibrant Rainbow Swirl Cupcakes!

Make the Cupcakes:

Step 1: Prepare Batter

Prepare the cake batter according to the box instructions.

Step 2: Divide and Color Batter

Divide the batter evenly among five bowls.

Add a few drops of red food coloring to one bowl, yellow to the second, green to the third, blue to the fourth, and two drops of blue plus two drops of red to the fifth (to create purple).

Stir each bowl until the color is evenly distributed, adjusting the amount of food coloring as needed to achieve your desired shades.

Step 3: Preheat and Prepare Pan

Preheat oven to 350° and line a muffin tin.

Step 4: Fill Cupcake Liners

Spray a muffin tin with cooking spray or line with cupcake liners.

Spoon a little of each color batter into each cup of the muffin tin, until they’re filled about two-thirds of the way up. You can layer the colors, swirl them slightly with a toothpick, or create any pattern you like.

Step 5: Bake

Bake the cupcakes according to the box instructions.

Let the cupcakes cool completely before frosting.

Make the Frosting:

Step 6: Beat Butter

In a large bowl using a hand mixer or in the bowl of a stand mixer using the whisk attachment, beat the softened butter until it’s light and fluffy.

Step 7: Add Sugar and Remaining Ingredients

Add the powdered sugar and beat on low speed until combined.

Whip in the vanilla extract, heavy cream, and salt.

(Add more heavy cream, 1 tablespoon at a time, if you’d like a thinner consistency.)

Step 8: Divide and Color Frosting

Divide the frosting into five bowls, adding food coloring to each and stirring, just like you did with the cake batter.

Step 9: Prepare Piping Bags

Place each color of frosting in a separate resealable sandwich bag and snip off one corner.

Step 10: Create Frosting Tube

Lay out a piece of plastic wrap.

Use each bag to pipe out a line of frosting in each color, side by side, on the plastic wrap.

Roll up the plastic wrap, creating a tube of frosting with all the colors lined up.

Twist the ends of the plastic wrap closed.

Step 11: Prepare Piping Bag

Slip a star tip onto one end of the frosting tube.

Trim the plastic wrap that sticks through the star tip.

Step 12: Frost and Serve

Pipe the rainbow swirl frosting onto the cooled cupcakes. Serve and enjoy!