Preheat oven to 160 C (320F). Arrange the garlic over the base of a baking dish. Rub olive oil all over pork and salt the skin. Place skin side down on the garlic cloves and cook for 3 hours. Increase the temperature to 180 C (355 F). Turn the pork over, add the sage between the garlic and the pork and cook for a further 30 minutes until skin is crunchy.
(We sometimes remove the skin and continue roasting whilst plating up the rest, just to make sure it's crispy).