In a microwave-safe mug, combine the flour, sugar, cocoa powder, baking powder, and salt.
Stir the dry ingredients until evenly mixed.
Add the milk, vegetable oil, and vanilla extract to the mug.
Mix until you have a smooth batter.
Optional: fold in chocolate chips or nuts.
Microwave the mug on high for 60-90 seconds.
Check for doneness; the cake should be set but slightly moist.
Let the mug cake cool for a minute before enjoying.
Top with whipped cream or fresh berries if desired.
Enjoy your delicious chocolate mug cake!