For the cupcakes:

1. In the bowl of a countertop mixer fitted with the paddle attachment, cream together the butter and sugar until light and fluffy (2-3 minutes on medium speed).
2. In a separate bowl, mix together the cake flour, baking powder, and salt.  Add the vanilla, egg whites, and ½ of the flour mixture to the mixer bowl.  Mix on low speed just until combined.
3. Add the remaining 1/2 of the flour mixture and mix on low until combined.
4. Add milk and mix on low until batter is fully combined.  (Don’t forget to scrape down the sides of the bowl with a spatula to ensure the batter is evenly mixed.)
5. Fold in the sprinkles.
6. Line a muffin tin with paper liners; fill each tin approximately 2/3 full.
7. Bake at 350°F for 26-28 minutes, or until a toothpick inserted into the center of the cupcake comes out clean.
8. Let cupcakes cool before frosting.

For the Frosting:

1. In the bowl of a countertop mixer fitted with the paddle attachment, add the butter and shortening and mix on high speed until fully combined.
2. Add the vanilla and powdered sugar 1 cup at a time, mixing after each addition until fully absorbed.
3. Add the milk 1 Tablespoon at a time until frosting reaches the desired consistency.
4. Frost cupcakes as desired; garnish with sprinkles.