Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius).

Melt butter in a large skillet.

Add chopped onion, celery, and tart apple to the skillet.

Cook the vegetables and apple until softened.

Remove from heat and stir in breadcrumbs.

In a large bowl, combine ground pork, sausage meat, parsley, ground sage, salt, and pepper.

Mix the pork and sausage mixture thoroughly.

Add the cooked vegetable and breadcrumb mixture to the meat mixture.

Combine the stuffing ingredients completely.

Salt and pepper the pork crown roast generously.

Rub the pork roast with a little ground sage.

Fill the center of the crown roast with the prepared stuffing, mounding the center slightly.

Cover the roast with foil, ensuring the bone ends are also wrapped with foil to prevent burning.

Roast in the preheated oven for 3 hours, or until a meat thermometer inserted into the thickest part of the roast reads 175 degrees Fahrenheit (80 degrees Celsius).

About 30 minutes before the roast is done, remove the foil from the stuffing to allow it to brown.

Transfer the roast to a large heated platter and remove the foil.

Add frills to each little 'leg' of the roast, if desired.

Let the meat rest for about 10 minutes before carving.

Decorate the platter with a round of small potatoes, large mushrooms, or cooked red cabbage.