Dry mushrooms on a clean kitchen towel or paper towel
Cut dry rough edge off the stems and discard Remove stems set aside these will be a part of the filling
Cook bacon until just done
Remove from grease.
Drain on paper towels.
Drain bacon grease, reserve 1 tbsp.
Chop the mushroom stems and cook in reserved grease.
Add a pinch of salt so they release their excess water.
Cook until browned and very tender.
Add onion and cook for about another minute until just to mellow out the raw flavor.
Put cooked bacon, cream cheese, mushroom, and onion mixture into a small food processor and blend until smoothish.
Line a jelly roll pan with parchment.
Fill each mushroom with just enough filling for a flat surface.
Add shredded Colby or cheddar cheese to the tops of each mushroom and bake at 350 until the mushrooms are very browned and tender and cheese is melted.
The pan will have water at the bottom.
You can serve on a serving platter or straight from the pan.