Preheat oven to 425 degrees F. Place lamb in a roasting pan. Rub or brush the rub mixture all over the lamb and roast 20 minutes. Reduce heat to 325 degrees F and cook lamb to desired degree of doneness, checking its progress with a meat thermometer. When inserted into the centre of the thickest part of the leg should read 140 degrees F for medium rare, 160 degrees F for medium and 170 degrees F for well done. Baste lamb occasionally with pan juices. Rest the lamb 10 minutes before slicing thinly.
To create some jus to serve with the lamb, remove excess fat from roasting pan and pour in stock. Bring to a simmer, season to taste, and serve.