Preheat oven to 350 degrees F. Line standard muffin tin with paper liners and set aside.

In a small bowl, whisk together milk, egg whites, and vanilla. Set aside.

In the bowl of stand mixer fitted with a paddle attachment (or using a hand mixer), cream together butter and sugar until smooth. Add liquids and mix on medium speed until combined. Scrape down bowl as needed to ensure thorough mixing.

In a large bowl, whisk together flour, baking powder, and salt. Add to mixing bowl in two additions, mixing on low speed. Fold in sprinkles.

 Even distribute cupcake batter among prepared muffin tin, filling them about two-thirds full. Bake for 20-25 minutes until toothpick inserted in center of cupcake comes out clean. Let cupcakes cool in tin for 10 minutes before removing from pan and allowing to cool on wire rack. Cupcakes may be frosted once they have cooled to room temperature.

In the bowl of stand mixer fitted with a paddle attachment (or using a hand mixer), cream butter until smooth. Add powdered sugar in three additions. Mix on low speed until thoroughly combined. Scrape down bowl as needed.

Add vanilla, pinch of salt, and 2 tablespoons cream. Mix on medium speed until buttercream is light and fluffy. If buttercream is too thick, add another tablespoon of cream.

Use a small cookie scoop to distribute buttercream among cooled cupcakes. Use a mini offset spatula (or the back of spoon) to level off buttercream. Decorate with sprinkles.