Pre-heat a cast iron Dutch oven, or large stockpot over medium-high heat. Season the beef pieces with salt and freshly ground black pepper. Add a little oil to the pot and brown the beef pieces well on all sides. Do this in batches so that you don’t over-crowd the pan. Set the browned beef aside while you finish browning all the beef.
Add the onion, celery and garlic to the Dutch oven and sauté for several minutes, until the onion has softened - about 5 minutes. Add the tomato paste and continue to cook for about 3 minutes to toast the tomato paste and continue to cook the vegetables.
Pour in the Guinness draft and deglaze the pan (scrape up any brown bits on the bottom of the Dutch oven with a flat spatula). Add the beef stock and return the browned beef to the Dutch oven. Bring the pot to a boil, reduce the heat, cover and simmer gently for 75 minutes. (gentle simmer = just a few bubbles, not a boil)
Add the carrots, potatoes and rutabaga, along with the thyme, bay leaves and Worcestershire sauce. Continue to gently simmer the stew, covered, for another 30 to 45 minutes. The beef should be tender, the potatoes, carrots and rutabaga should be soft and the sauce should thicken slightly.
Season to taste with salt, freshly ground black pepper and more Worcestershire sauce if desired. Garnish with the fresh parsley and serve with crusty bread to sop up the sauce at the end.