01 - Pat the chuck roast dry with paper towels and season all over with salt and pepper.
02 - In a large skillet over medium-high heat, heat 1 tablespoon oil. Sear the roast on all sides until browned, approximately 3-4 minutes per side. Transfer to the slow cooker.
03 - Scatter the carrots, potatoes, celery, onion, and garlic around and under the roast in the slow cooker.
04 - In a bowl, whisk together the beef broth, tomato paste, Worcestershire sauce, thyme, rosemary, and bay leaves. Pour over the roast and vegetables.
05 - Cover and cook on low for 8 hours, or until the beef is fork-tender and vegetables are soft.
06 - Remove the roast and vegetables to a platter. Discard bay leaves.
07 - Pour the cooking liquid into a saucepan. Skim excess fat if desired. In a small bowl, whisk cornstarch with cold water until smooth. Bring the cooking liquid to a simmer over medium heat, then whisk in the slurry. Cook until thickened, 3-5 minutes.
08 - Slice or shred the roast. Serve with vegetables and gravy ladled over the top. Garnish with chopped parsley if desired.