Pat beef chuck roast dry with paper towels. Season generously on all sides with kosher salt, black pepper, dried rosemary, and dried thyme.
Heat olive oil in a large skillet or Dutch oven over high heat until smoking hot. Sear the roast for 4 to 5 minutes per side until deeply browned with a dark caramelized crust. Transfer roast to the slow cooker crock.
Arrange halved red potatoes, baby carrots, and yellow onion wedges around the seared beef roast.
In a medium bowl or glass measuring cup, whisk together aged balsamic vinegar, clover honey, beef broth, minced garlic, Worcestershire sauce, and Dijon mustard until smooth.
Pour the honey balsamic mixture evenly over the beef roast and vegetables. Cover with the slow cooker lid and cook on LOW for 8 hours (or HIGH for 4.5 to 5 hours) until the beef is melt-in-your-mouth fork-tender.
Carefully transfer the beef and vegetables to a warm serving platter, tenting with foil. Shred the beef into large, succulent ribbons using two forks.
Pour the remaining cooking liquid from the slow cooker into a saucepan over medium-high heat. Whisk in the cornstarch slurry and simmer for 3 to 4 minutes until thick, glossy, and mahogany brown. Spoon the rich honey balsamic gravy generously over the shredded beef and vegetables. Garnish with fresh rosemary and serve hot!