Cupcakes:

2 large eggs, separated

2 1/4 cups sifted flour

2 1/2 teaspoons baking powder

1/2 teaspoon salt

3/4 cup unsalted butter, softened 

1 3/4 cups granulated sugar

3 teaspoons vanilla extract

1 cup whole milk

Milk Chocolate Frosting

1 cup unsalted butter, softened 

3 and 1/2 cups confectioners’ sugar

1/2 cup unsweetened cocoa powder

1/2 teaspoon salt

2 teaspoons vanilla extract

3 Tablespoons heavy cream

Rainbow sprinkles

Preheat the oven to 350°. Line a 12-count muffin pan with cupcake liners.  With a handheld or stand mixer fitted with a whisk attachment, beat 2 egg whites on high speed in a medium bowl until soft peaks form, about 2-3 minutes. Set aside.  Whisk the flour, baking powder, and salt together in a medium bowl. Set aside.  Using a handheld or stand mixer fitted with a paddle attachment, beat the butter on high speed until smooth and creamy – about 1 minute. Add the sugar and beat on high speed for 3-4 minutes until creamed together.  Scrape down the sides and up the bottom of the bowl with a rubber spatula as needed.  Add two egg yolks and the vanilla. Beat on medium-high speed until combined. Scrape down the sides and up the bottom of the bowl with a rubber spatula as needed. 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. Fold whipped egg whites into cupcake batter.  Spoon batter into cupcake liners filling halfway full. Bake for 18-21 minutes or until the tops of the cupcakes spring back when gently touched and a toothpick inserted in the center comes out clean. Allow to cool in the pan for 5 minutes, then transfer to a rack to cool completely.  Using a handheld or stand mixer fitted with a paddle attachment, beat the butter on high speed until smooth and creamy – about 2 full minutes. Turn speed to low and slowly add 3 cups of confectioners’ sugar, the cocoa powder, and salt. Beat until sugar/cocoa are absorbed into the butter, about 2 minutes. Turn the mixer to medium speed and add the vanilla and cream. Once added, turn the mixer to high speed and beat for 1 minute, adding more sugar if necessary.  Pipe or spread the frosting onto cooled cupcakes.  Decorate with sprinkles.