Preheat the oven to 475 degrees F. Place the roast in a small roasting pan. Brush with mustard; sprinkle with thyme, salt and pepper. Reduce the heat to 325 degrees F and roast to the desired doneness. 25 to 30 more minutes of cooking should yield a rare to medium rare roast. However, the best way to gauge doneness is to use an instant read meat thermometer. For rare beef, the centre of the roast should register 120 to 125 degrees F; for medium rare, 130 degrees F; and for medium, 140 degrees F. When cooked, transfer roast to a plate, tent with foil, and rest 10 minutes. While the meat rests, remove any excess fat from the juices in the pan then place over medium-high heat. Add the wine and green peppercorns and reduce wine by half. Add the stock and bring to a simmer. Adjust seasoning, and then serve slices of the beef with a container of the jus alongside for drizzling on top.
Note: Green peppercorns are sold in our pickle aisle.