Preheat oven to 350°F Prepare a cupcake pan with paper forms.
In a large bowl, cream together butter and sugar until very light and fluffy. Sift flour, baking powder, and salt together, and then blend into creamed mixture alternately with sparkling wine.
In another large clean bowl, beat egg whites until stiff peaks form. Fold 1/3 of the whites into batter to lighten it, then fold in remaining egg whites. Fill the cupcake liners about 2/3 full.
Bake for 20 minutes, or until a toothpick inserted into the cake comes out clean.
Make Butter Cream: With an electric mixer, beat together sugar and butter (or margarine). Mix on low until well blended, and then on medium for another two minutes. Add vanilla and champagne, beating on medium for another minute. Frost cupcakes!