Preheat the oven to 325 degrees F (165 degrees C).
Puncture the leg of lamb with the tip of a knife just far enough to insert slivers of garlic into the holes. Mix together the dill, salt and rosemary, and rub over the leg of lamb. Place the lamb, fatty side up, on a rack in a shallow roasting pan.
Roast uncovered for 2 to 2 1/2 hours in the preheated oven, to an internal temperature of 155 degrees F (68 degrees C) for medium. Tent with aluminum foil and let stand for 15 to 20 minutes before carving. The lamb will continue to cook a little bit, and the juices will set up better for carving.