01 - Preheat the oven to 325°F.
02 - Pat the beef roast dry with paper towels and season all sides generously with salt and black pepper.
03 - Heat vegetable oil in a large Dutch oven over medium-high heat. Sear the beef on all sides until deeply browned, about 4 to 5 minutes per side. Remove meat from pot and set aside.
04 - Add onions, celery, and garlic to the same pot. Sauté for 3 to 4 minutes until softened and fragrant.
05 - Stir in tomato paste and cook for 1 minute to develop flavor.
06 - Pour in Guinness stout, scraping up any browned bits from the bottom of the pot. Add beef broth and Worcestershire sauce, stirring to combine.
07 - Return the beef to the pot. Arrange carrots, potatoes, thyme, and bay leaves around the meat.
08 - Bring liquid to a simmer, cover tightly, and transfer to the oven. Cook for 2.5 to 3 hours until beef is fork-tender and vegetables are cooked through.
09 - Remove roast and vegetables to a serving platter. Discard bay leaves.
10 - Place the pot over medium heat on the stovetop. Stir in cornstarch slurry and simmer for 2 to 3 minutes until the gravy thickens to desired consistency.
11 - Slice or shred the beef. Serve alongside vegetables with generous ladles of gravy over the top.