Preheat your oven to 325°F (163°C) and line a 12-cup muffin tin with cupcake liners.

In a medium bowl, whisk together cake flour, baking powder, baking soda, and salt.

In a separate bowl, combine whole milk, sour cream, and vanilla extract, whisking until smooth.

In a large mixing bowl, cream the softened unsalted butter and granulated sugar together until light and fluffy.

Add the egg whites and mix until just combined.

Gradually add half of the wet mixture to the butter mixture, then half of the dry mixture, repeating with remaining ingredients.

Fill each cupcake liner about ¾ full with batter.

Bake for 20 to 22 minutes, checking for doneness.

Let the cupcakes cool on a wire rack for at least 10 minutes.

In a clean mixing bowl, beat together softened butter and powdered sugar until crumbly, then gradually add in whole milk and vanilla extract.

If desired, mix in gel food coloring for frosting.

Frost cooled cupcakes using a piping bag.