1. Preheat oven to 350 degrees. 2. In a medium sized bowl, whisk egg white and sugar until combined. Stir in melted butter and vanilla, then flour, baking powder. Add in milk and stir until smooth. 3. Add in any mix-ins, if desired. I added chocolate chips to one of mine. 3. Pour equally between 2 cupcake liners in a muffin pan. 4. Bake for 9-11 minutes, or until inserted toothpick comes out clean. Let cool completely, then frost, if desired, and enjoy!