01 - Preheat the oven to 325°F.
02 - Pat the beef roast dry and season all sides 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 browned, about 4–5 minutes per side. Remove and set aside.
04 - Add onions, celery, and garlic to the pot. Sauté for 3–4 minutes until softened.
05 - Stir in tomato paste and cook for 1 minute.
06 - Pour in Guinness stout if using, scraping up any browned bits from the bottom. Add beef broth and Worcestershire sauce.
07 - Return the beef to the pot. Add carrots, potatoes, thyme, and bay leaves, arranging vegetables around the meat.
08 - Bring to a simmer, cover, and transfer to the oven. Cook for 2.5 to 3 hours, or until beef is fork-tender and vegetables are cooked through.
09 - Remove roast and vegetables to a platter. Discard bay leaves.
10 - Place pot over medium heat. Stir in cornstarch slurry and simmer for 2–3 minutes until the gravy thickens.
11 - Slice or shred the beef. Serve with vegetables and spoon the gravy over the top.