Choose a microwave-safe 12-ounce cup or mug. Add the flour, sugar, cocoa powder, baking powder, and salt, then stir thoroughly so the cocoa and leavening are evenly distributed.

Pour in the milk, oil, and vanilla extract. Stir from the bottom and around the sides until no dry pockets remain, then fold in the chocolate chips.

Microwave the cup on high for 60 seconds. Check the center, then continue in 10-second bursts until the cake has risen and the top looks mostly set, usually 70 to 90 seconds total.

Let the cake rest in the cup for 1 minute because the interior will finish cooking from the residual heat. Serve warm with whipped cream, ice cream, powdered sugar, or a few extra chocolate chips.