In a microwave-safe mug (at least 12 oz capacity), combine 4 tablespoons of all-purpose flour, 4 tablespoons of granulated sugar, 2 tablespoons of unsweetened cocoa powder, 1/8 teaspoon of baking powder, and a pinch of salt. Stir well to combine dry ingredients.
Add 3 tablespoons of whole milk, 2 tablespoons of vegetable oil, and 1/4 teaspoon of vanilla extract to the mug. Mix thoroughly until the batter is smooth and free of lumps.
Stir in 2 tablespoons of chocolate chips evenly into the batter.
Microwave the mug on high power for 1 minute. Check the cake for doneness by inserting a toothpick into the center; it should come out clean or with a few moist crumbs.
If the cake is not fully cooked, microwave in additional 10-second intervals until done, being careful not to overcook.
Allow the cake to cool for 1-2 minutes before eating directly from the mug.