01 - Preheat the oven to 350°F. Grease and line three 8-inch round cake pans with parchment paper.
02 - In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.
03 - In a large bowl, beat the softened butter and granulated sugar using an electric mixer until light and fluffy, about 3-4 minutes.
04 - Add eggs one at a time, beating well after each addition. Mix in the cotton candy flavoring and vanilla extract until evenly combined.
05 - With the mixer on low speed, add the flour mixture in three parts, alternating with the milk, beginning and ending with the flour. Mix until just combined — do not overmix.
06 - Divide the batter evenly into two bowls. Tint one portion pink and the other blue with food coloring, adjusting intensity to your preference.
07 - Drop alternating spoonfuls of each colored batter into the prepared cake pans for a marbled effect. Swirl gently with a skewer or knife — do not over-swirl.
08 - Bake for 25-28 minutes, or until a toothpick inserted into the center of each layer comes out clean. Cool the cakes in their pans for 10 minutes, then invert onto a wire rack to cool completely.
09 - Beat the butter until creamy and smooth. Gradually add the sifted powdered sugar on low speed. Mix in the cotton candy flavoring and enough milk to reach a smooth, fluffy consistency. Divide the buttercream and tint one portion pink and the other blue.
10 - Once the cake layers are completely cool, stack and frost them with the pink and blue buttercream, swirling the two colors together for a cotton candy effect.
11 - Just before serving, crown the cake with fluffy pieces of fresh cotton candy. Serve immediately, as the cotton candy will dissolve upon contact with moisture.