Preheat oven to 350°F. Spray a 9x5 loaf pan with nonstick cooking spray (the kind with flour) or grease and flour it.
Whisk flour, baking powder, and salt in a medium bowl. Set aside.
Stir melted butter, sugar, and sour cream in a large bowl. Stir in eggs, one at a time, then stir in vanilla. Add champagne and dry ingredients and stir just until moistened. Pour into prepared pan.
Bake for 33-38 minutes, until a toothpick comes out clean. (Mine took 35 minutes.)
While the cake is baking, make the glaze. Heat the sugar and champagne in a small saucepan over medium heat until it boils. Boil for 1 minute, then remove from heat.
Cool for 15 minutes in the pan. Use a knife to loosen around the edges, then carefully remove the cake and place it on a cooling rack set over a cookie sheet. Use a pastry brush to brush the champagne glaze over the top of the cake. Let the cake finish cooling completely before frosting.
To make the frosting, whisk the powdered sugar, heavy whipping cream, and 1 tablespoon of champagne. Add more champagne as needed. Pour and spread over pound cake. Chill to set.