Preheat oven to 425 ℉. Remove stems from mushrooms. Chop enough to make 1 normal cup mushroomscooked stems and set aside. Melt 2 normal Tbsp unsalted butter butter in a saucepan over medium heat. Brush mushroom caps with butter and place top side down in a shallow baking pan. Melt remaining butter in same pan. Add chopped mushroom stems, onion and garlic powder and cook 4-5 minutes, or until tender. Stir in cream cheese, Parmesan cheese and parsley. Add stuffing. Mix lightly. Spoon about 1 Tbsp stuffing mixture into each mushroom cap. Bake 10 minutes, or until mushrooms are heated through.