In a small bowl, combine all frosting ingredients. Set aside.
In another bowl, combine all mug cake ingredients.
Spray the inside of a large mug with non-stick cooking spray. Pour cake mixture into the mug and microwave on high for 2 minutes and 15 seconds.
Remove the cake from the mug and allow to cool for about a minute. Cut the cake into two layers and frost between layers and on top. Serve immediately.