Make cupcakes. Preheat oven to 350°F and line muffin tin with cupcake liners.
In a medium bowl, whisk together flour, baking powder and salt. Set aside.
Using a stand mixer fitted with a paddle attachment, beat butter and sugar together until light and fluffy.
Add egg whites one at a time, mixing fully after each addition. Scrape down sides of bowl as needed. Mix in vanilla.
Alternating between the champagne and dry ingredients, gradually add ingredients, mixing until just combined. Do not overmix. Scrape down sides of bowl as needed.
Fill cupcake liners 2/3 full with batter. Bake 15-17 minutes, until inserted toothpick comes out clean. Let cupcakes cool completely.
Make the Buttercream. Using a stand mixer fitted with a paddle attachment, beat butter until creamy. Mix in raspberry puree and vanilla extract.
Gradually add powdered sugar one cup at a time. Slowly add champagne until desired consistency is achieved.
Place icing in piping bag fitted with a large round tip. Pipe frosting onto cupcakes and garnish with a raspberry. Refrigerate until ready to enjoy.