Preheat the oven to 325 degrees Fahrenheit, then prep three six-inch round cake pans with a swipe of shortening and dusting of flour to prevent sticking.

In a large bowl, whisk together the buttermilk, sour cream, egg whites, oil, vanilla, and cotton candy extract until thoroughly combined. Sift in the cake mix and whisk until just combined. Do not overmix. Gently stir in the sprinkles.

Split the batter evenly among the prepared pans. Bake for 27 to 30 minutes, until the center is baked through. Let the cakes cool in the pan for a minute before flipping them out onto a wire rack to cool completely. Wrap and freeze the cakes before assembly.

In the bowl of a stand mixer fitted with a paddle attachment, beat the butter on medium speed until it’s light and fluffy. Add the heavy cream, vanilla, cotton candy extract, and salt and beat again until combined, then scrape down the sides with a spatula. With the mixer on low speed, add the powdered sugar about half a cup at a time. The buttercream will be thick. Add a little more heavy cream, one tablespoon at a time, to thin it out if needed, and then flip the mixer to high speed and beat until the buttercream is lighter in color and texture, about two minutes

To each of two small bowls, transfer one cup of buttercream (two cups total). To one bowl, stir in the pink cotton candy and one drop of light pink gel coloring. To the other, stir in the blue cotton candy and one drop of light blue gel coloring. Transfer each color to a piping bag and set aside. Leave the rest of the buttercream white.

Place a cardboard cake round on a cake turntable. Dot a little bit of pink and blue entire cake buttercream in the center of the round and spread it out with an angled icing spatula.

Place the first chilled cake layer in the center. Add a layer of pink and blue buttercream. Place the next cake layer on top, then repeat, making sure to line the layers up evenly. After adding the top cake layer, crumb coat the cake by spreading a thin layer of white buttercream around the Freeze for two minutes to set the buttercream.

Using a wooden spoon, beat out any air bubbles in the remaining white buttercream. Finish frosting the cake as desired or follow the decorating instructions below.

Spread a final layer of white buttercream around the entire cake, using a stripe cake comb to create clean indents on the side of the cake. The crisper the indents, the cleaner the stripes will be later on. Freeze for at least 10 minutes so that the buttercream is very firm.

Pipe the pink and blue buttercream in the striped indents, and then immediately scrape the sides of the cake with a flat cake scraper. Apply a little bit of pressure and scrape until the clean stripes start to show through. Add the remaining buttercream (white, pink, and blue) to a piping bag fitted with a Wilton 6B tip. Pipe star dollops around the entire top of the cake.