Chop the centers to equal one and one-half cups. Blanch the cases for 5 minutes and turn upside down to drain. In a skillet, saute the chopped onion in one- fourth cup butter until lightly colored. Add the meat, crumbled, and cook a few minutes. Simmer about 5 minutes and add parsley, thyme, salt and pepper.
Fill shells with stuffing and put in a buttered shallow dish.
Pour the beef stock and wine around them. Bring to a boil on top of stove and then bake in a 350 degree F. oven, basting several times, for 45 minutes. Transfer the onions to a serving dish. Reduce the juices by half, pour over the onions and sprinkle with additional chopped parsley. In medium saucepan combine onions with water to cover.