Preheat the oven to 400°F (200°C).

Start by frying the bacon until really crispy. Let cool and crush into crumbs. Save the bacon fat.

Remove the mushroom stems and chop them finely. Sauté in the bacon fat, adding butter if needed.

Place the mushrooms in a greased baking dish.

In a bowl, mix the crumbled bacon with the fried, chopped mushroom stems and the remaining ingredients. Add some of the mix to each mushroom.

Bake for 20 minutes or until the mushrooms turn golden brown.