Season & Sear Beef: Pat the chuck roast completely dry with paper towels. Season all sides generously with kosher salt, black pepper, garlic powder, and onion powder. Heat olive oil in a heavy cast-iron skillet over medium-high heat until smoking. Sear the roast for 4 to 5 minutes per side until a deep, dark brown crust forms. Transfer the seared roast into a 6-quart or larger slow cooker.

Deglaze & Whisk Gravy Base: Lower the skillet heat to medium. Add tomato paste, Worcestershire sauce, and Dijon mustard, stirring for 1 minute. Pour in beef bone broth, scraping up all caramelized browned bits (fond) from the pan bottom. Bring to a gentle simmer for 2 minutes, then remove from heat.

Layer Vegetables & Herbs: Arrange the halved Yukon Gold potatoes, carrot chunks, thick onion wedges, and smashed garlic cloves evenly around and beneath the seared chuck roast in the slow cooker. Pour the warm skillet gravy mixture over the roast and vegetables. Tuck fresh rosemary sprigs, thyme sprigs, and bay leaves into the liquid.

Slow Cook to Fork-Tender: Cover tightly with the lid. Cook on LOW for 8 to 9 hours (or on HIGH for 5 to 6 hours) until the beef yields completely to a fork and breaks apart effortlessly into juicy, tender chunks.

Thicken Luxurious Gravy: Transfer the tender roast and vegetables to a warm serving platter and cover loosely with foil. Discard herb sprigs and bay leaves. Skim excess surface fat from the slow cooker juices. Whisk cornstarch slurry into the simmering juices and let cook on HIGH for 10 minutes until glossy, rich, and spoon-coating.

Shred & Serve: Gently pull the beef apart into generous succulent portions. Ladle the hot savory gravy lavishly over the meat, buttery potatoes, and sweet tender carrots. Garnish with fresh minced parsley and serve immediately.