Mix together all the dry ingredients in a small bowl except the sugar.
Now in your mug, mix together the butter and sugar until well combined (the sugar doesn't have to dissolve.) After, add in the egg and vanilla and mix again until well incorporated. Then add in the milk and mix again briefly.
Next, add in the dry ingredients and mix to form a batter. Once you have a smooth cake batter, add in the sprinkles (if using).
Microwave for 2 minutes. If after two minutes it is not done, microwave it using 10 second intervals till a toothpick comes out clean when pricked into the center. Let cool for one minute and enjoy warm or let cool completely and serve with a swirl of vanilla frosting and some sprinkles.