Heat oven to 325°F; season roast all over with salt and pepper.
Heat oil in a Dutch oven over medium-high heat. Sear beef 5 to 6 minutes per broad side until dark crust forms; transfer to a plate.
Cook onion in pot 5 minutes until edges brown. Stir in tomato paste and flour 1 minute.
Whisk in broth, scraping up every browned bit. Stir in Worcestershire, thyme, and bay leaf.
Return roast and juices; cover and oven-braise 2 hours.
Arrange carrots around beef; cover. Cook 60 to 90 minutes more until beef pulls apart with a fork and carrots are tender.
Transfer beef and carrots to a platter. Discard bay leaf; skim excess fat from liquid.
Simmer gravy on stovetop 5 to 10 minutes until it coats a spoon. Slice or pull roast; spoon gravy over it.