Remove meat from refrigerator and bring to room temperature. Rub the meat in oil, then season generously with salt and pepper.
In a large cast iron pan, heat oil on medium-high heat. Sear all sides of the meat, roughly 2-3 minutes each side. Remove the meat from the pan and turn the heat off.
Add onion, garlic, celery, carrots, and rosemary to the pan. Place the roast on top of the vegetables.
Bake at 325˚F for about 60 minutes (125˚F for rare doneness). If the vegetables look dry, add a little water to prevent burning.
Cover meat with tin foil and let rest for 30 minutes, while you make the gravy.
Sprinkle in flour and mash all the vegetables. Pour in ½ glass of red wine and let bubble for a minute or two. Add beef stock. Bring to a boil, then simmer until you reach your desired consistency. Using a sieve, remove excess bits from your gravy.