Preheat oven to 200°C/400°F/Gas Mark 6.

Wipe mushroom caps clean with a damp cloth. Remove stalks. Chop stalks and reserve 100 g (4 oz) for this recipe.

Remove casings from sausage. Crumble sausage into a frying pan and saute gently, adding a little olive oil if necessary, until meat is browned. Remove sausage with a slotted spoon and set aside.

Saute chopped mushroom stalks, onion, celery, green pepper and garlic in remaining fat, or add olive oil if needed. Cook until vegetables are tender, about 5 minutes. Add seasonings and mix well.

Add breadcrumbs, sausage and liquid. Mixture should be moist, but it won't adhere into a ball.

Lightly coat tops of mushroom caps with olive oil. Stuff caps with sausage mixture. Sprinkle with Parmesan cheese. Place mushrooms, stuffed side up, in shallow baking dish.

Bake at 200°C (400°F)Gas Mark 6 until cheese is browned and mushrooms are tender, about 15 minutes