Whisk in the butter and egg together. Stir in the milk, vanilla, and sugar until combined. Add in the our, baking powder, and salt. Microwave for about 75 seconds, and continue microwaving in 10- second increments until cooked through.
Top with vanilla or chocolate frosting or whipped cream and sprinkles.
QUICK TIP: Substitute almond extract for the vanilla extract for an Italian variety.