For the Funfetti Cake

1. Preheat your oven to 350 degrees Fahrenheit. Line a 9×13 cake pan with parchment paper and spray the paper with cooking spray to ensure the cake comes out cleanly.
2. In a medium-sized bowl, whisk all purpose flour, baking powder, baking soda, and salt together until combined.
3. In a large bowl, use a whisk to mix granulated sugar and room temperature eggs together for at least 2 minutes. The mixture should be come lighter in color, slightly puffy, and almost frothy. This creates a lighter, fluffier cake and is imperative for the success of the recipe.
4. Add slightly cooled melted butter, vegetable oil, room temperature buttermilk, vanilla extract, and butter extract to the egg and sugar mixture. Whisk until combined.
5. Slowly, add dry ingredients to the wet ingredients. Whisk carefully and do not mix past when the dry ingredients are fully incorporated and the batter is smooth.
6. Use a spatula to fold the sprinkles into the batter, making sure they disperse throughout the batter evenly.
7. Spread the batter into your prepared pan. Bake the cake for 25-35 minutes until the top is golden brown in color, the center of the cake springs back up when poked lightly with your pointer finger, and a toothpick inserted into the center of the cake comes out with moist crumbs on it.
8. Allow the cake to cool before frosting and decorating.

For the Buttercream + Decoration

1. In a large bowl with a hand mixer or in the bowl of a stand mixer fitted with a paddle attachment, beat room temperature unsalted butter until smooth.
2. Slowly, add powdered sugar to the butter, making sure not to add too much at once or mix on too high of a speed to avoid making a giant mess. Beat the powdered sugar into the butter until smooth.
3. Add vanilla extract and milk to the frosting and mix until incorporated.
4. Beat the frosting on high speed for 3-5 minutes until the frosting turns lighter and whiter in color, fluffier, and creamier. Scrape down the sides and bottom of the bowl as necessary to ensure the frosting is fully incorporated throughout.
5. Decorate the cooled cake as desired.
6. Store the cake at room temperature tightly covered or in an airtight container for up to 4 days.