Preheat the oven to 325°F (160°C) and line a muffin tin with cupcake liners.

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

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

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

Add the egg whites to the butter and sugar mixture and mix until fully combined.

Gradually add the dry ingredients and the wet mixture to the creamed butter, alternating between them.

Fill each cupcake liner about ¾ full with the batter.

Bake for 20-22 minutes, or until the tops spring back when touched, then cool.

Beat the unsalted butter until smooth.

Gradually add the powdered sugar, then mix in the whole milk until the frosting is creamy.

Add the red gel food coloring if desired, then frost the cooled cupcakes using a piping bag.

Serve and enjoy your delicious Copycat Magnolia Bakery Cupcakes!