01 - Rub the beef chuck roast evenly with kosher salt and black pepper on all sides.
02 - Heat a large skillet over medium-high heat. Sear the roast on all sides until browned, approximately 3-4 minutes per side. Transfer to the slow cooker.
03 - Place carrots, parsnips, potatoes, onion, celery, and garlic around and beneath the beef in the slow cooker.
04 - Whisk together beef broth, red wine, tomato paste, Worcestershire sauce, and Dijon mustard in a bowl until smooth.
05 - Pour the broth mixture over the beef and vegetables. Add rosemary, thyme, and bay leaves to the cooker.
06 - Cover and cook on LOW for 8-9 hours or HIGH for 4-5 hours until beef is fork-tender and vegetables are soft.
07 - Transfer the beef and vegetables to a serving platter. Discard bay leaves and herb stems.
08 - Skim excess fat from cooking liquid. Whisk cornstarch with cold water in a small bowl, then stir into the slow cooker. Cook on HIGH for 10-15 minutes until thickened.
09 - Slice or shred the beef. Arrange on plates with vegetables and spoon the thickened sauce over the top.