In a medium bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.
Add the buttermilk, milk, vanilla, and oil to the dry ingredients and beat with the paddle attachment of a stand mixer or a hand mixer just until fully combined. In a separate bowl whip the egg whites until you get medium-stiff peaks and gently fold into the batter.
Scoop the batter into the cupcake liners until they are ⅔ of the way full. Bake for 20-22 minutes, until a toothpick, comes out clean and the tops of the cupcakes bounce back when lightly pressed. Let the cupcakes cool.
Frost the cupcakes as desired and serve!
Add butter, powdered sugar, milk, vanilla, and salt to the stand mixer bowl. Stir to incorporate all the ingredients, then turn the mixer on high speed and beat until the frosting is white and fluffy about 10-15 minutes.