Step 1

Preheat the oven to 350°F. Line a 12-cup muffin pan with cupcake liners.

Step 2

In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.

Step 3

In a large bowl using a handheld or stand mixer fitted with a paddle attachment, beat the butter and sugar together on high speed until smooth and creamy, about 2 minutes. Scrape down the sides and bottom of the bowl as needed.

Step 4

Add the egg whites and vanilla extract. Beat on medium-high speed until combined, then beat in the sour cream. Scrape down the sides and bottom of the bowl as needed.

Step 5

With the mixer on low speed, add the dry ingredients in three additions alternating with the whole milk, beginning and ending with the dry ingredients, and mixing each addition just until incorporated. Do not overmix. Gently fold in the sprinkles.

Step 6

Pour/spoon the batter into the liners, filling them 2/3 full. Bake for 18-22 minutes, or until a toothpick inserted in the center comes out clean. Allow the cupcakes to cool completely before frosting.

Step 7

To make the frosting, in a large bowl using a handheld or stand mixer fitted with a paddle attachment, beat the butter on medium speed until creamy, about 2 minutes. Add confectioners' sugar, cream, vanilla extract, and salt. Beat on low speed for 30 seconds, then increase to high speed and beat for 2 full minutes. Add more confectioners' sugar if the frosting is too thin or more cream if the frosting is too thick.

Step 8

Frost the cooled cupcakes. Top with additional sprinkles. Enjoy!