For leg of lamb, gather one bone-in leg, 2 tablespoons garlic, 2 tablespoons rosemary sprigs, 2 tablespoons Dijon mustard and 1 cup chicken broth. Trim most the excess fat off the lamb, rub it with the herbs and mustard, and roast it for approximately 1 1/2 hours.
Remove the fell, the lamb's thin yet tough outer layer of fat. If you are unpracticed, the butcher may be willing to do so beforehand. However, leave enough fat below the fell to provide an outer crust for later broiling. With a sharp knife, create 1-inch incisions 1/2 inch deep all over the leg. Next, create a paste consisting of the garlic, mustard and herbs, along with 2 tablespoons salt, 2 teaspoons black pepper and 2 tablespoons olive oil. Rub it deeply into the lamb.
After allowing the lamb to marinate for about a half hour, transfer it to a roasting pan, and pour in the broth. Roast the lamb at 425 F for 20 minutes, and then reduce the heat to 325 F. With a meat thermometer inserted, monitor the meat until the internal temperature reaches between 130 and 135 F. This is medium-rare. Reset the oven to broil, and crisp the fatty outer layer of the lamb for approximately 5 minutes. Remove the lamb leg from the oven, and allow it to rest for at least 20 minutes before carving.