In a microwave-safe 12–16 oz mug, whisk flour, sugars, cocoa, and salt until combined.

Add oil, milk, and vanilla; stir until smooth and no dry streaks remain. Fold in chocolate chips if using.

Microwave on high for 45–60 seconds; check at 45s. The top should be set but slightly gooey. Avoid overcooking.

Let sit 1 minute, then enjoy straight from the mug or tip onto a plate.