Cut the lamb into thumb-sized cubes and toss in the flour with a teaspoon of salt and pepper.
Heat a large pan and add the olive oil. When the oil starts to smoke, add as many lamb pieces as will fit in one layer, cover with a lid and cook for a few minutes until soft and browned evenly. When coloured on all sides, remove from the pan. Repeat with the remaining cubes until they are all browned. Return all the lamb to the pan and turn the heat down.
Add the onion, celery, garlic, cinnamon, walnuts and bay leaves to the pan. Put the lid on and cook very gently for 3–5 minutes, until the onion is softened, stirring often to make sure nothing sticks.
Cut your pomegranates in half and juice them as you would an orange or lemon. You should get 2 ¾ cups or so of bright pink juice. (If you can’t find pomegranates, cranberry juice works well instead.) Add the juice to the lamb, reserving some pomegranate seeds. Top up with water to cover. Simmer very gently for 1½ hours, or until the lamb is tender, adding a little water now and then if the stew gets dry.
Remove the cinnamon stick and bay leaves and discard. Season to taste and sprinkle with the parsley and reserved pomegranate seeds. Serve with steaming hot saffron rice.