Preheat the oven to 350°F. Cut off the mushroom stalks and reserve. Arrange the mushroom caps in a buttered shallow dish, gill side up.
Heat 1 tablespoon of the oil in a frying pan and sauté the garlic briefly.
Finely chop the mushroom stalks and mix with the parsley and bread crumbs. Add the garlic and 1 tablespoon of the oil. Season with salt and pepper.
Pile a little of the mixture into each mushroom. Add the remaining oil to the dish and cover the mushrooms with buttered wax paper. Bake for 15-20 minutes, removing the paper for the last 5 minutes to brown the tops. Garnish with a sprig of the flat-leaf parsley.