01 - Set the oven to 320°F (160°C) to prepare for braising.
02 - Pat lamb pieces dry and season generously with salt and freshly ground black pepper.
03 - Heat olive oil in a large Dutch oven over medium-high heat and brown lamb in batches until evenly seared on all sides. Remove and set aside.
04 - Add chopped onion, sliced carrots, and celery to the pot and cook for 5 to 7 minutes until softened. Add minced garlic and cook for 1 additional minute.
05 - Stir in tomato paste and cook for 1 minute. Pour in dry red wine, scraping the pot bottom to deglaze and release browned bits.
06 - Return lamb to the pot, add beef or lamb stock along with rosemary, thyme, and bay leaves. Bring mixture to a gentle simmer.
07 - Cover the pot and transfer to the preheated oven. Cook for 2 to 2.5 hours until lamb becomes tender enough to pierce easily with a fork.
08 - Remove pot from oven and skim excess fat from surface. Optionally, stir in unsalted butter for added richness. Discard herb stems and bay leaves, then adjust seasoning.
09 - Serve the lamb hot, optionally garnished with fresh herbs, accompanied by mashed potatoes, polenta, or crusty bread.