Spinach-Stuffed Mushrooms

30 very lg. Mushroom caps
10 oz. pkg. frozen spinach, chopped
4 oz. ricotta cheese
1 sm. onion, finely chopped
1 t. butter

Wash and dry mushroom caps. Saute onion in butter until transparent. Mix cheese, onions and spinach, which has been
thawed and well drained. Stuff caps with mixture. Sprinkle each with grated Kefaloteri cheese. Bake in greased pan at
300 degrees for 25 minutes. Serve warm.