For the Cupcakes

1. Preheat your oven to 350 degrees Fahrenheit and line a 12-count muffin pan with liners.
2. In a large bowl, whisk vegetable oil, melted butter, granulated sugar, room temperature egg and egg yolk, vanilla extract, butter flavoring, and room temperature sour cream.
3. In a medium bowl, whisk flour, baking powder, and salt together.
4. Alternate adding dry ingredients and buttermilk to the wet ingredeints, starting and ending with the dry ingredients. Whisk until just combined, making sure not to overmix. Scrape down the sides as necessary.
5. Fold in rainbow sprinkles.
6. Fill liners with a little over 1/4 cup of batter.
7. Bake cupcakes for 18-23 minutes, or until a toothpick inserted into the center of the cupcakes comes out with moist crumbs. The tops should start to turn light golden brown and should spring right back up when poked.
8. Allow cupcakes to cool in the pan before frosting.

For the Frosting

1. In a large bowl with a hand mixer or in the bowl of your stand mixer fitted with the paddle attachment, cream the butter and shortening together until smooth.
2. Add powdered sugar slowly, and beat until fully combined.
3. Add vanilla extract and heavy whipping cream. Mix on high speed for 5 minutes to create a light, fluffy, airy, white, and smooth buttercream.
4. Frost cupcakes as desired.