01 - In a microwave-safe mug (minimum 12 oz), whisk together the gluten-free flour, cocoa powder, sugar, baking powder, and salt until well combined.
02 - Add the milk, vegetable oil, and vanilla extract. Mix with a fork until a smooth batter forms, making sure to scrape the sides and bottom of the mug.
03 - Stir in chocolate chips if using.
04 - Microwave on high for 1 minute. Check for doneness: the cake should be set but still moist in the center. If needed, microwave in 10-second increments until done (do not overcook).
05 - Allow to cool for 1-2 minutes before enjoying directly from the mug.