In a microwave-safe mug, combine the flour, sugar, cocoa powder, baking powder, and salt.
Stir the dry ingredients until evenly mixed.
Add milk, vegetable oil, and vanilla extract to the dry mix.
Mix well until a smooth batter forms.
Fold in chocolate chips or nuts if desired.
Microwave the mug on high for about 1 minute.
Check for doneness; the brownie should be soft but not liquid.
Let it cool for a minute before enjoying.
Top with ice cream or whipped cream if desired.
Dig in and savor your delicious treat!