Preheat an oven to 350F. Line a standard 12-cup muffin pan with paper or foil liners.
In a bowl, whisk together the flour, baking powder and salt. Set aside.
In a large bowl, using an electric mixer, beat together the sugar and butter on medium-high speed until light and fluffy, 2 to 3 minutes. Reduce the speed to low, add the egg and egg white one at a time, beating well after each addition, then beat in the vanilla.
Add the flour mixture in 3 additions, alternating with the champagne in 2 additions, beating until just combined. Scrape down the sides of the bowl as needed and be careful not to over beat.
Divide the batter evenly among the prepared muffin cups, filling each about three-fourths full (you should get about 11-12 cupcakes).
Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean.
- While the cupcakes are baking; in a small saucepan, bring the champagne to a boil over medium-high heat. Reduce to medium and allow to simmer until it reduces down to about 1/4 cup (about 8-10 minutes). Reserve 2 tablespoons of the reduction for the frosting, and use the rest to brush on top of the warm cupcakes. I brushed each cupcake twice with the reduction and discarded the leftover. Let cupcakes cool completely before frosting.
- In large bowl, using an electric mixer, beat the butter, powdered sugar, vanilla and 2 tablespoon of the champagne reduction until smooth. Frost as desired and sprinkle with sparking sugar.