This gluten-free mug cake is soft, tender, and delicious. Add sprinkles to turn the simple vanilla cake into a funfetti dream.
Spray a large (12 ounces) mug with nonstick cooking spray. Stir together gluten-free flour, sugar, and baking powder in the mug. Add egg, oil, milk, and vanilla extract. Stir until smooth with a fork or mini whisk. Stir in sprinkles if using.
Microwave on high for 60-80 seconds or until cake pulls away from the sides of the mug and the top looks dry. Allow cake to cool in the mug. Top warm cake with vanilla ice cream or whipped cream, if desired. Or allow the cake to cool and frost.
Preheat oven to 350 degrees. Follow step one above. Be sure to use an oven-safe mug. Place mug on a baking sheet. Bake until set, about 20 minutes.
Beat together the butter and powdered sugar until smooth with a spoon. Add milk. Mix until creamy. Spread frosting on cooled cake. If you put the frosting on the hot cake, it will melt.