In a small bowl, combine the flour, sugar, cocoa, and a pinch of salt.
Mix well to create a uniform dry mixture.
Add the milk, vegetable oil, and vanilla extract to the dry ingredients, and whisk until the mixture is smooth and free of lumps.
Pour the batter into a 12-ounce mug, leaving some space for it to rise.
Sprinkle chocolate chips on top of the batter to add a gooey texture when cooked.
Microwave the mug on high for about 1 to 2 minutes, or until the cake has puffed up and is set in the middle.