Using a paring knife make small slits into roast about 3-inches apart and press the garlic slivers into the slits. Using a pastry brush, coat the entire roast with the mustard. Sprinkle on the peppercorn and garlic marinade to completely cover the roast. Place on a rack in a roasting pan and cook until the thermometer inserted into the center reads 130 degrees F. Remove the roast from the oven, cover with foil and allow to rest for 10 to 15 minutes.
To make the Au Jus: Place the roasting pan over stovetop burners on medium low. Whisk in the worcestershire sauce and wine and scrape up the little brown bits from the bottom of the roasting pan. Reduce slightly and add the broth. Bring to a simmer and reduce slightly. Serve along with the sliced prime rib.