Preheat the oven to 220 deg/C. Mix together the spices and salt and rub all over the meat then put in a deep roasting pan and roast for 15 minutes.
Lower the oven temperature to 140 deg/C. Spread the onion and garlic around the meat. Add enough water to the pan so it comes halfway up the side. Seal tightly with tinfoil and roast for 4 1/2 to 5 hours.
Remove the pan from the oven. Take out the lamb and leave it to rest.
Remove the onin and garlic and push them through a sieve, saving the juices and discarding the onion and garlic. Cook the juice in a saucepan over a medium heat until it is reduced to about 1 1/2 cups of liquid.
Return the lamb to the roasting dish with a little of the reduced sauce. Cover tightly with tinfoil and return to the 140 deg/C oven for about 45 minutes until the lamb is hot all the way through.
Serve the lamb with the remaining sauce on the side.
From Cuisine, March 2014
Image courtesy of Flickr user Jeremy Keith and is used under a Creative Commons license.