01 - Season beef cubes evenly with salt and black pepper.
02 - Heat a large skillet over medium-high heat and brown beef cubes in batches to enhance flavor; transfer browned beef to slow cooker.
03 - Place carrots, parsnips, potatoes, onion, celery, and garlic into the slow cooker with beef.
04 - Whisk beef broth, red wine (if using), tomato paste, and Worcestershire sauce in a bowl; pour mixture over meat and vegetables.
05 - Add bay leaves, dried thyme, and dried rosemary; gently stir to combine all ingredients.
06 - Cover and cook on low setting for 8 hours or on high for 4 to 5 hours, until beef is tender and vegetables are cooked through.
07 - Thirty minutes before serving, create slurry by mixing cornstarch with cold water; stir into stew and cook on high until thickened.
08 - Remove bay leaves, adjust seasoning as needed, and serve warm.