Score skin of pork with sharp knife, and then remove the skin with about half a layer of fat underneath. (In one piece if possible). Place this on a shallow baking tray, sprinkle generously with salt then put it on the highest shelf of the over for 15-20 mins until it is a very crisp & crunchy piece of crackling.
Remove from oven and drain off the fat into a bowl.
Place breadcrumbs in a mixing bowl, crush the peppercorns with a pestle and mortar and add them to the breadcrumbs together with sage and a half teaspoon of salt.
Spread the mustard over the layer of fat on the pork, and then press the breadcrumb mixture firmly all over making sure that is well coated.
Transfer the joint to a roasting tin and place a square of foil lightly on top.
Place the meat on a high shelf in the oven. Reduce the heat to 190ºC and roast the pork for about 2 hours, basting occasionally, and removing the foil for the last 30 minutes.
When the pork is cooked, remove from the tin and leave it in a warm place to relax, then spoon off the fat from the roasting tin. Sprinkling a little flour into the juices and make some gravy with the cider.
To garnish: core the apples (do not peel), cut into rings and fry gently in butter fill tender.
Serve the pork cut into slices with some gravy, crackling and apple rings.