Grease a 12-ounce (or larger) mug with nonstick cooking spray or butter. Set aside.
In a separate mixing bowl, whisk together the flour, unsweetened cocoa powder, granulated sugar, baking powder, and salt until well combined. Add the milk, oil, and pure vanilla extract and continue mixing until fully combined.
Pour the batter into the prepared mug and sprinkle the chocolate chips on top.
Transfer the mug with the batter to the microwave and microwave for 60-90 seconds or until the center of the cake is just set.
Carefully remove from the microwave (the mug will be hot!) and allow to cool slightly, then top with your favorite toppings, and enjoy!