Combine all in a microwave-safe mug (at least 2 inches / 5 cm wide at the base).
Mix with a fork until the batter is smooth and fully incorporated, then flatten the top with the back of a spoon.
Place the mug in the microwave and cook on high for 1 minute and 30 seconds.
Carefully remove the mug and test for doneness by inserting a toothpick into the center. If it comes out clean, it's ready. If wet batter clings to the toothpick, microwave for an additional 15 to 30 seconds.
Invert the mug over a plate and give it a gentle shake to release the biscuit.
Serve warm, slathered with your favorite fat like butter or coconut oil if desired.