Preheat the oven to 350?F (177?C). Line a 12-count muffin pan with cupcake liners and a second pan with 2 liners.

Whisk the cake flour, baking powder, baking soda, and salt together. Set aside.

Using a handheld or stand mixer, beat the butter on high speed until smooth and creamy, about 1 minute.

Add the sugar and beat on high speed for 2 minutes until creamed together. Scrape down the bowl as needed.

Add the egg whites and vanilla extract; beat on medium-high speed until combined. Then, beat in the sour cream.

With the mixer on low speed, add the dry ingredients until just incorporated. Slowly pour in the champagne until combined.

Pour/spoon the batter into the liners, filling them only 2/3 full. Bake for 19-22 minutes, or until a toothpick inserted in the center comes out clean.

Allow the cupcakes to cool completely before frosting.

In a small saucepan, bring the champagne to a boil over medium-high heat. Simmer until reduced to 1/4 cup, about 7-10 minutes. Set aside to cool completely.

In a large bowl, beat the butter on high speed until completely smooth and creamy, about 2-3 minutes.

Gradually add the confectioners? sugar, beating on low at first and then increasing to high speed.

Once creamy, beat in 3 tablespoons of the reduced champagne and the vanilla extract.

Frost the cooled cupcakes using a Wilton 1M piping tip. Top with sprinkles as desired.