Preheat oven to 325°F (160°C).
- Season lamb shanks with salt and pepper. Heat olive oil in a large Dutch oven and sear shanks on all sides until browned. Remove and set aside.
- Add chopped onion, celery, and garlic to the pot. Sauté for 5 minutes until softened.
- Stir in tomato paste and cook for 1–2 minutes to deepen flavor.
- Pour in red wine, scraping the bottom of the pot. Let it simmer to reduce slightly.
- Add stock, rosemary, thyme, and bay leaves. Return lamb shanks to the pot, submerging them as much as possible.
- Cover and transfer to the oven. Braise for 2.5 to 3 hours, until lamb is tender and falling off the bone.
- In the last hour of cooking, add chopped carrots, parsnips, and turnips. Stir and return to oven.
- Once done, remove bay leaves and herb stems. Adjust seasoning if needed. Serve hot with mashed potatoes or crusty bread.