Preheat your oven to 350°F (175°C). Grease and flour two 8-inch round cake pans. Spray a cake pop pan or silicone sphere mold with nonstick cooking spray.

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

In a large mixing bowl, beat the softened butter and sugar together until light and fluffy. Add eggs one at a time, mixing well after each addition. Stir in vanilla extract.

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

Divide a portion of the batter into separate bowls, depending on how many colors you want for the polka dots. Add a few drops of gel food coloring to each bowl and mix until the colors are vibrant.

Spoon the colored batter into the cake pop pan or silicone sphere mold, filling each cavity about 3/4 full. Bake the spheres for 12-15 minutes or until a toothpick inserted into the center comes out clean. Let cool completely.

Pour a thin layer of the uncolored batter into one of the prepared round cake pans. Arrange the cooled cake spheres (polka dots) randomly over the batter in a single layer. Pour more batter over the spheres, ensuring they are completely covered. Repeat this process with the second cake pan.

Bake the round cakes 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 to a wire rack to cool completely.

For the frosting, beat the powdered sugar and softened butter together in a mixing bowl. Add the milk and vanilla extract gradually, beating until smooth and spreadable.

Once the cakes are cool, spread a layer of frosting on top of one cake layer. Stack the second cake layer on top and frost the top and sides of the cake. Decorate as desired.