Add the butter and cream cheese to a mug and microwave for 20 seconds.
Mix with a fork.Add the baking powder, coconut flour and stevia and combine with fork.Add the egg and combine.Add the salt and fresh blueberries, and gently combine.
Microwave for 2 minutes.Flip over onto a plate or eat right out of the mug.
Dust with powdered erythritol, if desired and enjoy!