1. Pat the lamb pieces dry with paper towels, then season them with the salt and black pepper and toss with the flour until evenly coated.

2. Heat the olive oil in a large heavy Dutch oven over medium high heat. Add the bacon if using and cook until it begins to crisp and render its fat. Working in batches, sear the floured lamb pieces in the hot fat until well browned on all sides, then transfer them to a plate and set aside.

3. Reduce the heat to medium and add the onion, carrots, celery, and parsnip or turnip to the pot. Cook, stirring often, until the vegetables soften and start to brown around the edges, about 5 to 7 minutes. Stir in the garlic and tomato paste and cook for 1 to 2 minutes more until fragrant.

4. Pour in the red wine if using and stir, scraping up any browned bits from the bottom of the pot. Let the wine simmer for 2 to 3 minutes to reduce slightly.

5. Add the beef or lamb broth, Worcestershire sauce, rosemary, thyme, and bay leaves. Return the browned lamb and any accumulated juices to the pot and stir to combine.

6. Bring the mixture to a gentle boil, then reduce the heat to low, cover with a lid, and simmer for 45 minutes.

7. Stir in the potatoes, re cover the pot, and continue simmering for another 45 minutes to 1 hour, or until the lamb is very tender and the vegetables are cooked through.

8. Check the consistency of the stew. If you prefer it thicker, lightly mash a few of the potatoes in the pot or simmer uncovered for a few extra minutes to reduce the liquid.

9. Taste and adjust seasoning with additional salt and pepper as needed. Remove the bay leaves and any woody herb stems.

10. Stir in the chopped fresh parsley just before serving and ladle the lamb stew into bowls, garnishing with extra parsley if desired.