Preheat your oven to 325°F while lining a 12-cup muffin tin with cupcake liners.

In a bowl, whisk together 2 cups of cake flour, 1.5 teaspoons of baking powder, 0.5 teaspoon of baking soda, and 0.5 teaspoon of salt.

In another bowl, whisk together 1 cup of whole milk, 0.5 cup of sour cream, and 1 tablespoon of vanilla extract until well blended.

Cream together 0.5 cup of room-temperature unsalted butter and 1.5 cups of granulated sugar for about 3–5 minutes until light and fluffy.

Add in 4 large egg whites, mixing well until fully incorporated, about 2 minutes.

Gradually add the wet ingredients to the creamed butter mixture, alternating with the dry ingredients, until combined.

Fill each cupcake liner about ¾ full with the batter using a cookie scoop.

Bake for 20–22 minutes or until the tops spring back lightly and a toothpick comes out clean.

Let the cupcakes cool in the tin for about 5 minutes, then transfer to a wire rack to cool completely.

Beat together 0.5 cup of unsalted butter and 4 cups of powdered sugar, adding 3–4 tablespoons of milk and 1 teaspoon of vanilla extract until smooth.

If desired, add gel food coloring, then frost the cooled cupcakes with the buttercream.