In a coffee mug or other large mug, mix 4 Tbsp. vegetable oil and 3 Tbsp. cocoa powder until you have a thick, chocolatey liquid.
2 tablespoon vegetable oil, 3 tablespoon cocoa powder
Add in ¼ tsp. salt and 6 Tbsp. sugar and thoroughly mix through until smooth.
¼ teaspoon salt, 6 tablespoon sugar
Using a fork, thoroughly mix in 1 egg.
Carefully stir in 4 Tbsp. flour and ¼ tsp. baking powder. Thoroughly mix together.
4 tablespoon flour, ¼ teaspoon baking powder
Fold in 2 Tbsp. white chocolate chips and 2 Tbsp. milk or semi-sweet chocolate chips (optional) until evenly distributed.
2 tablespoon milk or semi-sweet chocolate chips, 2 tablespoon white chocolate chips
Microwave for 1 minute. The brownie in a mug will rise, then sink a little bit, and should still be wet to the touch.