To make stuffing: Melt butter in a large frying pan over medium heat. When foam subsides, add onion and fry, stirring frequently, for about 5 minutes.
Stir in celery and apples; cook (without browning) about 5 minutes longer. Scrape frying pan contents into a large mixing bowl. Add breadcrumbs, minced pork, sausage meat, parsley, sage, salt and pepper. Mix together gently but thoroughly.
Fill the centre of the crown with the stuffing, mounding it slightly. Cover it with a round of aluminium foil and wrap the ends of the chop bones in strips of foil to prevent them from charring and snapping off.
Place the crown on a rack in a shallow roasting pan just large enough to hold it comfortably, and roast in the centre of the oven, undisturbed, for about 3 hours or until internal temperature of meat is 80 C. (Note: 30 minutes before pork is done, remove the foil from the top of the stuffing to allow the top to brown.)
Carefully transfer the crown to a large, heated circular platter. Let the crown rest for about 10 minutes, remove all foil, and then carve.