Place the pork on a clean work surface, with a sharp knife make scores about a centimeter apart through the skin into the fat, but be careful not to make it to deep. Rub the salt into the scores pulling the skin apart to make sure the salt is in. Make sure you brush off the excess salt, turn it over. Then season with a pinch of salt and pepper again. Place the pork, skin-side up in a roasting tray and place it in the preheated oven. Roast for 30 minutes, until the skin of the pork has started to puff and you can see it turning in crackling. At this point, turn the heat down to 170C, cover the meat with tinfoil, place it back in the oven for about 4 1/2 hours.