Heat oven to 325° Fry bacon in a large, heavy-duty skillet over medium-heat. Remove the bacon and set aside, leaving bacon fat in skillet.
Season beef with salt and pepper. Fry in the bacon fat until beef is browned on all sides. Remove from skillet and set aside.
In the same skillet, fry the onion, celery, and carrots for about 5 minutes. Add a small amount of oil if necessary. Add garlic, turnips and parsnips. Season with salt and pepper to taste, fry for another 3 to 5 minutes.
Add the tomato paste and stir to incorporate. Slowly pour in the Guinness, Worcestershire sauce. Bring to a simmer over low heat, scraping up the browned bits from the bottom and sides of skillet.
Add beef and bacon back to the skillet. Stir in 2 cups beef broth, mixing well. Remove from heat and pour beef mixture into a oven-proof Dutch oven. Add remaining beef stock and more if mixture appears to thick.
Add bay leaves, fresh thyme sprigs. Season with salt and pepper. Stir in cremini mushrooms. Tuck the cabbage wedges into the stew.
Cover tightly and Bake at 325° for 2 hours and stew is thick and meat and vegetables are tender.