Cook onions in boiling salted water for 15 minutes. Rinse under cold water, drain and dry. Cut a slice off top of each and scoop out the centres with a spoon. Place upside down. Finely chop half the scooped out onion. Add to the ham, cheese, egg and bread, season with salt and pepper. Mix well and fill the onions. Grease a baking dish, put in the filled onions. Dot with butter and moisten the onions with the chicken stock. Bake for 40 minutes at 180c. Basting from time to time with the juice from the dish.
