Preheat the oven to 450 degrees F. Combine the first 5 ingredients in a small bowl. Place the roast in a roasting pan; brush with the mustard mixture. Roast for 10 minutes, and then reduce the heat to 325 degrees F. Roast 65 minutes more. This should yield a rare to medium-rare roast; if you like your beef medium in doneness, cook 10 to 15 minutes longer. Set the roast on a plate, tent with foil, and rest 10 minutes. Set the roasting pan on the stovetop over medium-high heat. Add the stock/flour mixture and bring to a simmer, scrapping the bottom of the pan to release the tasty brown bits. Simmer until a lightly thickened gravy forms. Slice the meat and serve the gravy alongside.