01 - In a microwave-safe mug (at least 12 ounces), whisk together the gluten-free flour, cocoa powder, sugar, baking powder, and salt.
02 - Pour in the milk, oil, and vanilla extract. Stir thoroughly until a smooth, lump-free batter forms.
03 - Fold in the chocolate chips if desired.
04 - Microwave on high power for 1 minute and 30 seconds to 2 minutes, or until the top is set and springs back lightly when touched. Cooking times may vary depending on microwave wattage.
05 - Allow the cake to rest for 1 to 2 minutes before serving. Top with whipped cream or fresh berries if desired.