Heat the oven to 200C (180C fan)/390F/gas 6. Put the chopped onion, garlic, ginger, spices and 10g each of the dill and parsley in a food processor and blitz until finely minced. Add the oil, vinegar, a teaspoon and three-quarters of salt and a generous grind of pepper, and blitz to a coarse paste. Pat dry the lamb, pierce the flesh all over with the tip of a small, sharp knife (about 10-12 times in all), then coat the lamb with the paste. You can now cook it right away, or refrigerate and marinate for a few hours to overnight.
Put the onion wedges, cinnamon sticks, cardamom and the fig quarters in a large, ovenproof, cast-iron saucepan for which you have a lid (about 28cm in diameter). Lay the lamb fatty side up on top, then pour in the chicken stock around the edges so as not to wash off the marinade. Bake uncovered for 45 minutes, baste the lamb with the juices, then cover with a lid, lower the heat to 160C (140C fan)/310F/gas 2½ and roast for four hours, basting it three or four times while it’s cooking. Turn the heat back up to 200C (180C fan)/390F/gas 6, remove the lid and roast for 45 minutes more, or until the lamb is well browned and extremely tender, and the sauce has reduced nicely.
Gently lift the lamb out of the pot and leave it to rest in a large oven tray. Pour the remaining contents of the pot into a large, shallow platter or dish with a slight lip, then put the lamb on top.
Combine the chopped figs with the pistachios, lemon juice and remaining herbs, spoon this mix all over the lamb and serve with the lemon wedges alongside.