Preheat the oven to 450 degrees F.
Set the roast in roasting pan. Brush with the mustard, and then sprinkle with the rosemary, salt and pepper. Roast for 15 minutes, and then reduce the oven temperature to 325 degrees F. For a rare to medium rare prime rib, roast 75 minutes more, or until the centre of the roast reaches 130 degrees F on an instant-read meat thermometer. When the beef is ready, transfer to a plate, tent with foil and rest 10 minutes.
To make the jus, remove excess fat from the roasting pan and then set over mediumhigh heat. Add the wine and peppercorns and reduce the wine by half. Add the stock/cornstarch mixture, bring to a simmer, and simmer 5 minutes. Taste the jus and season as needed. Slice the beef and serve the jus alongside.