Preheat your oven to 350°F (175°C). Grease and line two 9-inch round cake pans with parchment paper.

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

In a large mixing bowl, cream the butter and sugar together until light and fluffy using an electric mixer.

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

Gradually add the dry ingredients to the wet ingredients, alternating with the milk. Begin and end with the dry mixture, mixing until just combined.

Gently fold 1 cup of rainbow sprinkles into the batter using a spatula.

Divide the batter evenly between the two prepared cake pans. Place the pre-made cake balls randomly in the batter in both pans, ensuring they are spaced apart.

Bake the 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 them to a wire rack to cool completely.

Spread a layer of buttercream frosting on top of one cake layer, then carefully place the second layer on top.

Frost the entire cake with the buttercream, smoothing it evenly across the top and sides.

Decorate the cake generously with additional rainbow sprinkles, pressing them gently into the frosting to adhere.

Slice and serve to reveal the colorful polka dot cake balls hidden inside!