Preheat oven to 375 degrees. ... heat. Add the mushrooms and saute until lightly browned, ... mix. Pour the gratin mixture into a buttered, shallow ... 6 to 8 servings.
Saute butter, onion, mushrooms until onions become clear, about ... Pour into individual au gratin dishes. Sprinkle with bread crumbs, ... 6 to 8 servings.