Heat 1 Tbsp olive oil in a large skillet over medium-high heat. Season the beef chuck roast with salt and pepper. Sear the roast on all sides until browned, about 4-5 minutes per side. Transfer to slow cooker.

In the same skillet, add remaining 1 Tbsp olive oil. Add chopped onion and cook for 2 minutes. Add minced garlic and cook for 30 seconds. Pour mixture over the beef in the slow cooker.

Pour beef broth over the ingredients in the slow cooker. Stir in Worcestershire sauce, thyme, and rosemary. Cover and cook on low for 8-9 hours until beef is tender.

Add quartered potatoes and sliced carrots to the slow cooker. Cover and continue cooking until vegetables are tender, approximately 1 hour.

Remove the beef and vegetables from the slow cooker. Shred the beef and cut potatoes if desired.

To thicken the gravy, whisk cornstarch with 3 Tbsp beef broth to make a slurry. Pour into a small saucepan and bring to a simmer, stirring constantly, for 30-60 seconds.

Pour the gravy over the shredded beef and vegetables. Garnish with chopped parsley before serving.