Use a sharp cook’s knife to make 6-9 small but deep cuts in the lamb, through to the bone. Sit in a shallow-sided baking dish.
Mix the olive paste, garlic and rosemary together and spoon or press small spoonfuls into each cut, spreading the rest over the lamb. Cover loosely with foil.
Roast in the preheated oven for 2½-3 hours (or until the meat begins to fall from the bone), removing the foil in the last 30 minutes of cooking time. Remove from the oven and allow to sit for 20 minutes, reserving the juices.
Carve the lamb into chunky pieces, place on a serving plate with your own choice of salad ingredients and drizzle over the reserved juices.
In a food processor, process ¾ cup stoned black olives with 2-4 anchovy fillets, 1-1½ Tbsp olive oil and 1 Tbsp lemon juice until smooth.
Shoulder of lamb often comes pre-boned and tied for roasting. To prepare this recipe using a boned-out shoulder, untie the meat, spread the olive mixture over the meat and cook for about 2½ hours.
Use a leg of if wished; cooking time will be about the same.