Place the butter in a 12-oz. mug and microwave for about 30 seconds, or until melted.
If the butter is hot, allow it to cool to room temperature.
Add the egg to the butter and beat well.
Mix in the Keto Chow, allulose, almond flour, coconut flour, and baking powder.
Sprinkle the blueberries over the surface of the batter. They will sink in as the muffin cooks.
Microwave on full power for 60-90 seconds* or until the muffin is risen and shrinks away from the sides of the mug.
Let the muffin cool for two minutes before removing it from the mug.