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, approximately 4 to 5 minutes per side. Remove the meat from the 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 deepen the flavor.
06 - Pour in Guinness stout if using, 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. Add carrots, potatoes, thyme, and bay leaves, arranging vegetables around the meat.
08 - Bring the liquid to a simmer, cover tightly, and transfer to the preheated oven. Cook for 2.5 to 3 hours, or until beef is fork-tender and vegetables are completely cooked through.
09 - Transfer the roast and vegetables to a serving platter. Discard the bay leaves.
10 - Place the pot over medium heat on the stovetop. Stir in the cornstarch slurry and simmer for 2 to 3 minutes until the gravy thickens to desired consistency.
11 - Slice or shred the beef. Arrange on plates with vegetables and spoon the rich gravy generously over the top.