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

Add the remaining 0.5 tablespoon olive oil to the same pot. Saute the diced onion for 2 minutes, then add the minced garlic and cook for 30 seconds until fragrant. Pour over the roast in the slow cooker.

Return the pot to heat. Add 1.25 cups beef broth, Worcestershire sauce, fresh thyme, and fresh rosemary. Cook for 15 seconds, scraping up all browned bits from the bottom. Remove from heat.

Layer the halved Yukon Gold potatoes and carrot chunks over the onion mixture. Pour the deglazed broth and herb mixture evenly over the top. Season with additional salt and pepper.

Cover and cook on LOW for 8 to 9 hours until the roast and vegetables are tender. Do not lift the lid during cooking.

Remove the roast and vegetables. Let the roast rest a few minutes, then shred it, discarding large pieces of fat. Cut potatoes further if desired.

Optional Gravy: Strain the crockpot broth into a small saucepan and bring to a simmer. Whisk cornstarch with 3 tablespoons cold beef broth until smooth. Pour into the saucepan and stir constantly for 30 to 60 seconds until thickened. Add a pat of butter for richness.

Plate the shredded beef and vegetables, spoon the gravy over the top, and garnish with fresh parsley.