In a microwave-safe mug, combine flour, sugar, cocoa powder, baking powder, and salt.
Mix well to ensure no lumps remain.
Add milk, vegetable oil, and vanilla extract to the dry ingredients.
Stir until the mixture is smooth and well combined.
Fold in chocolate chips or nuts if desired.
Microwave on high for 1 minute.
Check for doneness and microwave for an additional 15-30 seconds if needed.
Let it cool for a few minutes.
Top with whipped cream, fresh fruits, or chocolate syrup.
Enjoy your quick and delicious mug cake!