01 - Preheat the oven to 325°F.
02 - Pat the lamb dry and season generously with salt and freshly ground black pepper.
03 - Heat olive oil in a large ovenproof pot or Dutch oven over medium-high heat. Sear the lamb on all sides until browned, about 3 to 4 minutes per side. Remove and set aside.
04 - In the same pot, add onions, carrots, celery, and garlic. Sauté for 5 to 6 minutes until softened and lightly browned.
05 - Stir in tomato paste and cook for 1 minute to develop flavor.
06 - Pour in dry red wine, scraping up browned bits from the bottom. Simmer for 2 minutes to reduce slightly.
07 - Return the lamb to the pot. Add beef or lamb stock, rosemary, thyme, and bay leaves. Bring to a gentle simmer.
08 - Cover the pot tightly and transfer to the preheated oven. Cook for 4 to 4.5 hours, occasionally basting with pan juices, until the lamb is tender and falls apart easily.
09 - Remove the lamb and vegetables to a serving platter. Skim excess fat from the cooking liquid and reduce on the stove if a thicker sauce is desired.
10 - Serve the lamb with vegetables, spooning over the rich sauce.