Heat 1 tablespoon olive oil in a large pot over medium-high heat. Pat the chuck roast dry with paper towels, then season it all over with salt and ground black pepper. Sear the roast in the hot pot until nicely browned on both sides, about 4 to 5 minutes per side. Transfer the browned roast to the slow cooker.

Add the remaining 1/2 tablespoon olive oil to the same pot. Saute the diced onion for about 2 minutes, then add the minced garlic and cook for 30 seconds more until fragrant. Pour the onion and garlic mixture over the roast in the slow cooker. Return the pot to the heat. Add 1 1/4 cups beef broth, Worcestershire sauce, thyme, and rosemary. Cook for about 15 seconds, scraping up any browned bits from the bottom of the pot for extra flavor. Remove pot from heat.

Layer the halved Yukon Gold potatoes and carrot chunks evenly over the onion mixture in the slow cooker. Pour the deglazed broth and herb mixture from the pot evenly over the top. Sprinkle with additional salt and ground black pepper. Cover and cook on low heat until the roast and vegetables are tender, about 8 to 9 hours.

Once everything is tender, carefully remove the roast and vegetables from the slow cooker. Shred the roast, discarding any large pieces of fat, and cut the potatoes further if desired. I like to let the roast rest for a few minutes before shredding, which keeps it juicy and easy to handle.

If you prefer a thicker sauce, strain the broth from the slow cooker into a small saucepan. Bring the broth to a simmer over medium-high heat. In a small bowl, whisk the cornstarch with 3 tablespoons beef broth until smooth, then pour the mixture into the saucepan. Stir constantly and let simmer for 30 to 60 seconds until the gravy thickens. For extra richness, you can add a pat of butter to the finished gravy.

Arrange the shredded roast and vegetables on serving plates. Pour the homemade gravy over the top and sprinkle with fresh parsley to finish. I like to be generous with the parsley, as it brings a burst of freshness and color to the dish.