Wash the champignons and remove their stems.
Dig out some of the inside with a small spoon. Put a little butter in each mushroom and bake them at 392°F (200 °C) for 10 min.
Take them out and fill them with the finely chopped bacon. Cover each mushroom with grated cheese and sprinkle with parsley.
Turn the oven on the top element only and return the mushrooms to the oven for the cheese to crisp.