01 - Preheat the oven to 425°F.
02 - Rub the beef roast with olive oil, salt, pepper, thyme, and minced garlic.
03 - Place the roast on a rack in a large roasting pan.
04 - Toss potatoes, carrots, parsnips, and onion with olive oil, salt, and pepper. Arrange around the beef in the pan.
05 - Roast in the oven for 20 minutes at 425°F.
06 - Lower temperature to 350°F and continue roasting for 1 hour 10 minutes for medium doneness. Use a meat thermometer for accuracy: 140°F for medium rare.
07 - Remove beef and vegetables from the oven. Rest the beef, loosely covered with foil, for 15 minutes before slicing.
08 - Place roasting pan over medium heat on the stove. Melt butter, then whisk in flour and cook for 1 minute. Gradually add beef stock, whisking to deglaze the pan and scrape up browned bits. Add Worcestershire sauce if using. Simmer until thickened, about 5 minutes. Strain if desired.
09 - Slice the beef and serve with roasted vegetables and hot gravy.