01 - Pat the beef roast dry with paper towels and season all sides generously with kosher salt and freshly ground black pepper.
02 - Heat a large skillet over medium-high heat. Sear the roast on all sides until deeply browned, about 2-3 minutes per side. Transfer to the slow cooker.
03 - Place carrots, parsnips, potatoes, onions, celery, and garlic around and beneath the roast in the slow cooker.
04 - Whisk together beef broth, red wine, tomato paste, and Worcestershire sauce in a bowl until smooth. Pour over the meat and vegetables.
05 - Scatter dried thyme and bay leaves over the top of the ingredients.
06 - Cover and cook on low heat for 8 hours, or until beef is fork-tender and vegetables are completely cooked through.
07 - Remove roast and vegetables, cover to keep warm. Strain cooking liquid into a saucepan. Whisk cornstarch and cold water together, then stir into the liquid. Simmer over medium heat until thickened, 2-3 minutes.
08 - Slice the beef roast against the grain. Serve with vegetables and spoon gravy over portions. Garnish with chopped fresh parsley.