Trim any excess fat from lamb shanks and season generously with salt.

Mix together the cinnamon, nutmeg, cardamom, black pepper and turmeric. Sprinkle evenly over shanks and rub into meat. Let sit at room temperature at least an hour, or wrap and refrigerate overnight, then bring to room temperature.

Place a deep, heavy pot over medium-high heat and add oil to a depth of 1/2 inch. When oil is hot, add 2 lamb shanks and fry until nicely browned on all sides, about 5 minutes. Remove and set aside, then brown the 2 remaining shanks.

Meanwhile, put saffron in a small bowl with lime juice, 2 teaspoons rosewater and 1/2 cup warm water. Let steep for 10 minutes. Heat oven to 350°F/180°C.

Carefully remove all but 2 tablespoons oil from Dutch oven. Add chopped onion and cook over medium heat until softened and lightly colored, 8 to 10 minutes.

Season onion with salt, then add lime zest, orange zest, thyme sprigs and bay leaves. Stir in saffron mixture. Lay in the lamb shanks and add the broth. Bring to a boil, then turn off heat and cover pot.

Transfer pot to oven and bake for about 1 1/2 hours, covered, until meat is tender and beginning to fall from the bone.

Remove lamb shanks to a deep serving dish and keep warm. Strain braising juices through a fine-mesh sieve into a bowl, pressing with a wooden spoon to obtain all the liquid (discard thyme, bay leaves and onions).

Skim fat, then taste and add salt if necessary. Add 1 more teaspoon rosewater, if desired. Reheat strained juices and pour over lamb shanks. Combine parsley, mint and reserved orange zest and sprinkle over top.

Accompany with saffron basmati rice.