To prep, the mushrooms, remove the stems and chop them up.
Melt the butter in a large saucepan over medium heat. Slowly cook and stir the chopped mushroom stems and onion, until the onion softens. Remove from the heat.
Stir the filling of mushroom stems, bacon, and 1 c. of the total cheddar cheese together. Fill each mushroom cap.
Bake the mushrooms for 15 minutes, or until the cheese has melted and the mushrooms are heated through.
Sprinkle with the remaining cheese to serve. Enjoy!
