01 - Pat the beef roast dry with paper towels. Season all sides generously with salt and 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 - In a bowl, whisk together beef broth, tomato paste, Worcestershire sauce, thyme, and rosemary until smooth. Pour over the beef and vegetables. Tuck bay leaves into the liquid.
06 - Cover and cook on low setting for 8 hours, or until the beef is fork-tender and shreds easily.
07 - Carefully remove the roast and vegetables to a serving platter. Cover loosely to keep warm.
08 - For a thicker sauce, skim excess fat from the 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 against the grain. Arrange with vegetables on plates, spoon sauce generously over the top, and garnish with fresh chopped parsley.