In a ramekin or mug, mix the mashed banana, egg, and coconut flour together.
Microwave on high for 1 to 2 minutes, checking for doneness. Cooking time may vary based on your microwave's wattage.
Gently take the dish out of the microwave and place it on a rack to cool. You can enjoy it directly from the mug or remove it to serve.
Notes
You’ll want to use a very ripe, sweet banana since there is no sugar added.Overcooking mug cakes leads to a rubbery texture, so be sure to remove the cake when it's still slightly gooey in the center.A medium banana typically weighs around 60 grams, so you might need slightly more or less depending on its size.