Preheat oven to 350 degrees F. Line muffin tins with cupcake liners (12 regular, 24 mini, or a combo of 6 regular and 12 minis).
In a mixing bowl, combine flour, baking powder, baking soda, and salt.
In another bowl, melt butter and whisk in the sugar, buttermilk, sour cream, and vanilla. Add the liquid ingredients to the dry and mix until just combined. Set aside.
With an electric mixer, beat egg whites until soft peaks form. Fold into the batter until combined.
Spoon batter into cupcake liners (I like to use an ice cream scoop).
Mix sugar and cinnamon together and sprinkle 1/2 teaspoon on the top of batter. Reserve remaining.
Bake for 15-18 minutes until toothpick comes out clean. (If you are baking mini and regular cupcakes, bake the mini ones first and then the regular.) Leave in tin for a couple minutes until able to remove onto a wire rack. Cool completely before frosting.
For the Frosting:
In a mixing bowl, beat butter and cream cheese with an electric mixer on medium speed. Add the powdered sugar a little at a time and beat until smooth and creamy. Mix in the vanilla extract.
Place frosting in a piping bag fitted with a 1M star tip. Swirl frosting on top of each cupcake and then sprinkle the remaining cinnamon sugar mixture on top.