01 - Pat the beef roast dry with paper towels. Season all sides generously with kosher salt and black pepper.
02 - Heat olive oil in a large skillet over medium-high heat. Sear the roast on all sides until deeply browned, about 3–4 minutes per side.
03 - Place carrots, parsnips, turnips, onion, garlic, celery, and potatoes in the bottom of a 6–8 quart slow cooker.
04 - Transfer the seared beef roast on top of the vegetable bed.
05 - Whisk together beef broth, tomato paste, Worcestershire sauce, dried thyme, and dried rosemary in a bowl until smooth.
06 - Pour the sauce mixture over the beef and vegetables. Tuck bay leaves into the liquid. Cover and cook on low for 8 hours, or until beef is fork-tender.
07 - Remove the roast and vegetables to a serving platter. Cover loosely with foil to keep warm while preparing the sauce.
08 - For thicker gravy, skim excess fat from cooking liquid. Whisk cornstarch with cold water until smooth, then stir into the slow cooker. Set to high and cook uncovered for 10–15 minutes until thickened.
09 - Slice or shred the beef. Arrange with vegetables on plates, spoon sauce generously over top, and garnish with chopped fresh parsley.