01 - Pat the beef roast thoroughly dry with paper towels. Generously season all sides with kosher salt and freshly ground black pepper, pressing the seasoning into the meat.
02 - Heat a large skillet over medium-high heat until hot. Sear the roast on all sides until deeply browned, approximately 2-3 minutes per side. Transfer the seared beef to the slow cooker.
03 - Place carrots, parsnips, potatoes, onions, celery, and garlic around and underneath the roast in the slow cooker, distributing them evenly.
04 - In a mixing bowl, whisk together beef broth, red wine, tomato paste, and Worcestershire sauce until thoroughly combined. Pour the mixture evenly over the meat and vegetables.
05 - Scatter dried thyme and bay leaves across the top of the ingredients.
06 - Cover the slow cooker with its lid. Cook on low setting for 8 hours, or until beef is fork-tender and vegetables are completely cooked through.
07 - For thicker gravy, carefully remove the roast and vegetables to a serving platter and cover to keep warm. Strain the cooking liquid into a saucepan. Whisk cornstarch and cold water together until smooth, then stir into the hot liquid. Simmer over medium heat, whisking constantly, until thickened, 2-3 minutes.
08 - Slice the beef roast against the grain. Arrange meat and vegetables on serving plates. Spoon gravy generously over the top and garnish with chopped fresh parsley.