01 - Preheat the oven to 325°F (165°C).
02 - Generously season the lamb leg with salt and freshly ground black pepper.
03 - Heat olive oil in a large Dutch oven over medium-high heat. Sear the lamb on all sides until deeply browned, approximately 10 minutes. Remove and set aside.
04 - Add onions, carrots, parsnips, celery, and garlic to the pot. Sauté for 5 minutes until vegetables soften slightly.
05 - Stir in tomato paste and cook for 1 minute to enhance flavor.
06 - Pour in dry red wine, scraping the bottom of the pot to loosen browned bits. Simmer for 2 minutes to reduce slightly.
07 - Return the lamb to the pot. Add beef or lamb stock, rosemary, thyme, and bay leaves. Ensure the liquid comes halfway up the lamb; add more stock if necessary.
08 - Bring to a simmer on the stovetop. Cover with a tight-fitting lid and transfer to the oven. Braise for 2 to 2½ hours, or until the lamb is fork-tender.
09 - Remove lamb and vegetables to a serving platter. Skim excess fat from the sauce and reduce over medium heat if a thicker consistency is desired.
10 - Slice or shred the lamb and serve alongside the vegetables. Spoon the sauce over the dish.