Clean mushrooms and remove stems. Set caps aside. Finely chop stems. In a skillet, melt butter and lightly saute mushroom stems. Add cheese, celery salt onion, A1 Steak Sauce, chopped parsley, and garlic salt. Mix well. Stuff each mushroom with hot mixture. Mix bread crumbs with melted butter; top each mushroom with buttered crumbs.
Set caps on well-greased baking sheet. Broil for 3-5 minutes, or until tops are browned. Serve hot. Makes 24 appetizers. These may be made ahead and refrigerated until ready for heating and serving.