3In a microwave-safe mug, combine the all-purpose flour, granulated sugar, unsweetened cocoa powder, baking powder, and salt. Mix well.
Add the milk, vegetable oil, and vanilla extract to the dry ingredients. Stir until the mixture is smooth and well combined.
Microwave the mug on high for 1 minute and 30 seconds to 2 minutes, or until the brownie has risen and is set in the middle.
Allow the brownie to cool for a few minutes before enjoying. Optionally, you can top it with a scoop of ice cream or a dollop of whipped cream.