Preheat the oven to 350˚F/175°C. Line a 8x8 inch baking pan with parchment paper or grease well with cooking spray.
In a large bowl, whisk flour, baking powder, baking soda and salt together to combine. Set aside.
In a large mixing bowl using an electric hand mixer (or stand mixer), beat the butter, oil and sugar on medium speed until fluffy and light. Add eggs, one at a time, beating well with each addition. Remember to scrape down the bowl as needed. Add vanilla extract and beat until combined.
With the mixer on low speed, add half of the dry ingredients and beat just until combined. Add milk and beat until combined. Add the other half of the dry ingredients and beat slowly or fold by hand only until combined. Add in sprinkles and gently fold with a rubber spatula. The batter should be smooth and completely incorporated. Do not over mix.
Spread the cake batter into the prepared pan. Smooth it out into a thin, even layer with a rubber spatula. Bake for 20-25 minutes or until the top is lightly browned and a toothpick inserted in the center comes out clean. Remove the cake from oven and allow it to cook in cake pans for 10-15 minutes before transferring to cool completely on a wire rack. The cake must be cool completely or chilled in the fridge for at least 1 hour before applying frosting.