1In the food processor, process the salt, rosemary,and garlic until they're as finely minced as possible. Add the mustard and balsamic vinegar and process for 1 minute.
2Place lamb in a roasting pan with the ribs curving down,and coat the tops with the mustard mixture. Allow to stand for 1 hour at room temperature.
3Heat oven to 450*.
Roast lamb for exactly 20 minutes for rare, or 25 minutes for medium rare.
Remove from oven and cover with foil. Allow to sit for 15 minutes. then cut into individual ribs and serve.