01 - In a microwave-safe mug (at least 12 ounces), whisk together the gluten-free flour blend, cocoa powder, sugar, baking powder, and salt until uniformly combined.
02 - Add the milk, vegetable oil, and vanilla extract to the mug. Stir with a fork until a smooth, lump-free batter forms, scraping the sides and bottom thoroughly.
03 - Gently fold in the chocolate chips, if using, distributing them evenly throughout the batter.
04 - Microwave on high power for 1 minute. The cake should appear set on the edges while remaining slightly moist in the center. If underdone, continue microwaving in 10-second intervals until just set, taking care not to overcook.
05 - Let the cake rest in the mug for 1 to 2 minutes before serving. Enjoy warm directly from the mug or invert onto a small plate.