Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans and set them aside.

In a medium bowl, whisk together the flour, baking powder, and salt.

In a large mixing bowl, cream the softened butter and sugar together until light and fluffy using a hand mixer or stand mixer.

Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.

Alternately add the dry ingredients and milk to the butter mixture, beginning and ending with the dry ingredients. Mix until just combined.

Divide a small portion (about 1 cup) of the batter into separate bowls for each food coloring color you want to use. Add a few drops of food coloring to each bowl and mix until the color is uniform.

Scoop the colored batter into spherical silicone molds or small pans designed for baking cake balls. Bake these colored cake balls at 350°F (175°C) for about 10-12 minutes, or until a toothpick inserted comes out clean. Allow them to cool completely.

Pour a thin layer of the uncolored cake batter into the bottom of one prepared cake pan. Arrange the cooled cake balls (colored polka dots) randomly across the batter. Cover the cake balls with more uncolored batter, ensuring they are fully submerged.

Repeat the process with the second cake pan.

Bake the assembled cakes in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out clean.

Let the cakes cool in the pans for 10 minutes, then transfer them to wire racks to cool completely.

Once cooled, frost the cakes with vanilla buttercream frosting. Stack the cakes and coat the top and sides evenly with frosting.

Decorate the outside as desired and serve slices that reveal the colorful polka dots inside!