Steps
1. In a microwave-safe mug, combine flour, sugar, cocoa powder, baking powder, and salt.
2. Add milk, vegetable oil, and vanilla extract to the dry ingredients. Stir until smooth and no lumps remain.
3. If desired, fold in chocolate chips or nuts.
4. Microwave on high for 70-90 seconds, or until the cake has risen and is set but still moist.
5. Let cool for a minute before enjoying directly from the mug.