A good leg of lamb comes from a sheep less than 1 year old. If the sheep is over a year old, the meat should be labeled mutton. Mutton has a stronger flavor than lamb, so look for a leg from a young lamb. Fresh lamb should be pink and firm to the touch.
Things You'll Need
1 leg of lamb, bone-in
2 tablespoons olive oil
2 tablespoons minced garlic, optional
salt and freshly ground pepper, to taste
2 tablespoons fresh rosemary
Allow the leg of lamb to rest on the counter for 30 minutes to bring it to room temperature.
Preheat the oven to 325 degrees F.
Rub the lamb with the olive oil and spread it with the garlic. Salt and pepper as desired.
Pierce the lamb with a knife, creating slits all over the surface. Push some rosemary into the slits, then spread the remaining rosemary over the lamb.
Place the leg of lamb in a large roasting pan. Cook at 325 degrees until it's as well done as you like it. Medium rare registers 145 degrees F on a meat thermometer, medium is 155 degrees, and well done is 170 degrees. The temperature will continue to rise as the lamb rests in the next step, so remove it when its still a few degrees below the desired temperature. Cooking time will be approximately 1 1/2 to 3 hours, depending on the size of the leg of lamb and the desired degree of doneness.
Remove the lamb to a serving platter and cover loosely with aluminum foil. Let it rest for 10 to 15 minutes, which seals in the juices. Slice thinly and serve.