In an 8-12 oz microwave safe mug, combine the all-purpose flour, unsweetened cocoa powder, brown sugar, baking powder, and salt. Mix until well combined.
Add the milk, vegetable oil, and vanilla extract. Mix until well combined.
Top the brownie with chocolate chips.
Place mug with brownie batter in the microwave and cook on high for 1 minute and 45 seconds, adding a few more seconds if batter has a lot of wetness on the top of the brownie.