• Preheat the oven to 350 F. Prepare 2 standard cupcake pans by lining with cupcake liners.
• In a mixing bowl, mix all dry ingredients on low speed to blend. Add the soft butter and mix until evenly crumbly, like fine damp sand. 
• Add the egg whites one at a time, then the whole egg, beating well after each addition to begin building the structure of the cake. Scrape down the sides and bottoms of the bowl after each addition/
• In a small bowl, whisk the milk with the vanilla extract. Add this mixture, 1/3 at a time, to the batter. Beat 1 to 2 minutes after each addition, until fluffy. Be sure to scrape down the sides and bottom after each addition in the bowl.
• Pour the batter into the prepared pans. Bake for 20 minutes. A toothpick or cake tester inserted in the center will come out clean when done. Remove from oven, remove from pan, and cool on a rack. Frost with white chocolate peppermint buttercream.

White Chocolate Peppermint Buttercream

• In a large mixing bowl, using a handheld electric mixer at medium speed, cream butter until light and creamy. Beat in the melted white chocolate. 
• Add the confectioners' sugar and peppermint extract and beat a low speed, scraping sides and bottom of bowl, until light and fluffy.