Preheat oven to 350°F. Peel onions and boil whole for 10 minutes in a stainless steel pan. Core center of onion with spoon, leaving shell. Chop centers finely, add rest of ingredients, mix well, stuff mixture into shells. Reserve broth and butter. Place in greased 3 quart baking dish, moisten each onion with broth, dot with butter, and bake in a 350°F oven for 20 minutes. Serves 6.