All credit here to Yotam Ottolenghi, Its so good I didn't even want to adapt it a little. Best to marinate the meat in the spices the day before, so this recipe takes some time, however the small amount of effort is definitely worth it! I personally have cooked this several times for parties and it is an absolute hit every time. I nearly always do extra to enjoy over the next few days, it is especially delicious in a sandwich, wrapped in a flatbread or packed into a pita pocket.
1 leg of lamb, on the bone
2 teaspoons black peppercorns
1⁄2 teaspoon cardamom pods
1⁄4 teaspoon fenugreek seeds
1 teaspoon fennel seeds
1 tablespoon cumin seeds
1 star anise
1⁄2 cinnamon stick
1 tablespoon grated nutmeg, about half a pod
1⁄4 teaspoon ground ginger
1 tablespoon sweet paprika
1 tablespoon dried sumac
3⁄4 tablespoon kosher salt
1 3-inch piece of fresh ginger, peeled and grated
3 garlic cloves, peeled and crushed
3⁄4 cup chopped cilantro, stems and leaves included 4 tablespoons fresh-squeezed lemon juice
1⁄2 cup peanut or other neutral oil
Put the peppercorns, cloves, cardamom, fenugreek, fennel, cumin, star anise and cinnamon in a cast-iron pan set over medium-high heat and dry-roast them for a minute or two, until the spices begin to pop and release their aromas. Take care not to burn them. Add the nutmeg, ground ginger and paprika, and toss for a few more seconds, just to heat them, then transfer to a spice grinder. Process the spices into powder. Transfer to a medium bowl, and stir in the sumac, salt, fresh ginger, garlic, cilantro, lemon juice and oil, and stir to combine.
Use a small sharp knife to score the leg of lamb in a few places, making half-inch-deep slits through the fat and meat. Put the lamb in a large roasting pan and rub the marinade all over it, using your hands to massage the meat. Turn the lamb fat-side up, cover the pan with aluminium foil and place it aside on a countertop for at least a couple of hours, or preferably, rest it overnight in the refrigerator.
Heat oven to 140. Remove the foil and place the lamb in the oven. Roast for approximately 4-5 hours, or until the meat is completely tender. After 30 minutes of roasting, add about a cup of boiling water to the pan, and use this liquid to baste the meat every hour or so. (Add more water, as needed, making sure there is always a little in the bottom of the pan.) After 90 minutes or so, cover the lamb with aluminium foil to prevent the spices from burning. Once the lamb is done, remove it from the oven, and leave to rest for 10 to 15 minutes before carving and serving.