Preheat oven to 400F. Rub the pork roast with pepper, salt, cayenne, and sugar. Place in an oven proof dish and cook for 20 minutes. Pour the apple juice over the top and reduce heat to 325F. Spread 2 tbsp. of the butter and the rosemary over the roast. Cook 30 minutes per lb of roast. Baste every 20 minutes (using juice in the pan). When roast is done, remove from the oven and let stand for 15 minutes. For gravy, pour pan juices into a small pot, add stock and remaining 2 tbsp. of butter. Boil for 2 minutes, until it has thickened slightly.