Preheat your oven to 350°F (175°C) and grease a 9×13-inch baking pan.

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

In another bowl, cream the softened butter and sugar until light and fluffy.

Add eggs one at a time along with vanilla extract; mix until well combined.

Gradually incorporate the dry ingredients into the wet mixture, alternating with milk until just combined. Gently fold in rainbow sprinkles.

Pour the batter into the prepared pan and spread evenly. Bake for 25-30 minutes or until a toothpick inserted comes out clean. Allow cooling completely before frosting.