Preheat oven to 325°F. Position a rack in the lower-middle.
Pat the roast dry. Season all over with salt and pepper.
Heat oil in a large Dutch oven over medium-high heat. Sear roast on all sides until deeply browned.
Transfer roast to a plate. Add onion, carrots, and celery to the pot. Cook until softened, 4–5 minutes.
Stir in garlic and tomato paste. Cook 1 minute, stirring to coat the vegetables.
Pour in red wine to deglaze. Scrape up browned bits and simmer 2 minutes to reduce slightly.
Return roast with its juices. Add broth, Worcestershire, thyme, and rosemary. Bring to a gentle simmer.
Nestle potatoes around the roast. The liquid should come about halfway up the meat.
Cover and braise in the oven until fork-tender, about 3 hours, turning the roast once halfway.
Set roast on a board to rest. Skim fat. Whisk flour with water; stir into simmering juices to thicken. Slice and serve with vegetables and gravy. Garnish with parsley.