01 - Rub the chuck roast evenly with kosher salt and freshly ground black pepper on all sides to enhance flavor during cooking.
02 - Heat a large skillet over medium-high heat. Sear the seasoned roast on all sides until a deep brown crust forms, approximately 3-4 minutes per side. Transfer the seared beef to the slow cooker.
03 - Place the carrots, parsnips, Yukon Gold potatoes, yellow onion wedges, celery pieces, and smashed garlic cloves around and beneath the beef in the slow cooker insert.
04 - In a mixing bowl, whisk together the beef broth, dry red wine (if using), tomato paste, Worcestershire sauce, and Dijon mustard until fully incorporated and smooth.
05 - Pour the broth mixture evenly over the beef and vegetables. Add the fresh rosemary sprigs, thyme sprigs, and bay leaves to the cooker.
06 - Cover the slow cooker with its lid. Cook on LOW setting for 8 to 9 hours, or on HIGH for 4 to 5 hours, until the beef shreds easily with a fork and vegetables are tender.
07 - Transfer the beef roast and cooked vegetables to a serving platter using tongs. Discard the bay leaves and herb stems from the cooking liquid.
08 - Skim any excess fat from the surface of the cooking liquid. Whisk together cornstarch and cold water in a small bowl until smooth, then stir into the slow cooker. Cook on HIGH for 10 to 15 minutes until the sauce reaches desired consistency.
09 - Slice or shred the beef against the grain. Serve portions of meat and vegetables on plates, spooning the thickened sauce generously over each serving.