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