In a mug, mix together all dry ingredients (flour, sugar, baking powder, and salt).
Melt butter in a microwave-safe bowl.
Add melted butter, milk, and vanilla extract to the dry ingredients, mix until combined. Then, add candy sprinkles, mix. The mixture will fill about half of the mug. It’s ok when the cake will be baked, the dough will rise.
Cook a mug cake in a microwave for 70 seconds, allow cooling in a microwave for 1 minute. Then, check if it set, if no, cook for another 15-30 seconds. Enjoy!