In a microwave-safe mug, combine flour, sugar, cocoa powder, baking powder, and salt.
Mix the dry ingredients thoroughly with a fork.
Add milk, vegetable oil, and vanilla extract to the mug.
Stir until the ingredients are well combined and no dry flour remains.
If desired, fold in chocolate chips or berries.
Microwave the mug on high for 1 minute.
Check the cake; if it’s still wet, microwave in 10-second intervals until cooked.
Let it cool for a minute before adding toppings.
Top with whipped cream or your choice of toppings.
Enjoy your delicious mug cake straight from the mug!