Season beef with salt, including the rack of bones. Rub mustard all over beef; sprinkle with rosemary and pepper. Set beef in a 12x14-inch roasting pan. Cover loosely with plastic wrap and refrigerate for 2-3 days.
Remove beef from refrigerator 3 hours before you are ready to roast it, to allow it to come to room temperature.
Arrange rack in lower third of over and heat to 450°F.
Roast the beef, rib side up, until it begins to brown and sizzle, 20-25 minutes. Reduce heat to 325°F; continue roasting until a meat thermometer inserted in the thickest part of the meat registers 120°F for medium rare, about 2 hours.
Transfer roast to a carving board and let rest for 25-30 minutes. Remove and discard chine bone. Carve roast and serve with reserved pan juices.