Preheat the oven to 350º F. Line a muffin pan with muffin liners.

In a mixing bowl combine the butter and sugar, beat using an electric mixer, 1-2 minutes until fluffy. Add in the egg whites, sour cream, milk, and vanilla extract. Beat lightly with the electric mixer.

In a separate mixing bowl combine the flour, cinnamon, baking powder, and salt. Sift the dry ingredients together, this will help produce extra fluffy cupcakes. Gradually add the flour mixture to the wet ingredients a few spoonfuls at a time. Mix until just incorporated. Fill the muffin liners 1/2 full.

Bake for 17-19 minutes at 350º F or until a few moist crumbs remain on a toothpick when inserted into the center. Allow the cupcakes to cool completely before adding the frosting.

Place room temperature unsalted butter and cream cheese in a mixing bowl. Use an electric mixer on medium and beat together for 1-2 minutes, until whipped and fluffy.

Add in the vanilla extract, powdered sugar, and cinnamon, beat again on low for 1-2 minutes, scraping down the sides of the bowl, until everything is incorporated.

If the frosting is too thick, add a splash of milk or heavy cream, beat until creamy.

Transfer the frosting to a piping bag fitted with an open star piping tip (similar to a Wilton 1M). Pipe the frosting onto the cupcakes. Sprinkle cinnamon sugar over the cupcakes. Top with churro pieces if desired.