01 - Preheat oven to 325°F (160°C).
02 - Pat lamb shanks dry and season evenly with salt and freshly ground black pepper.
03 - Heat olive oil in a large Dutch oven or ovenproof pot over medium-high heat. Brown lamb shanks on all sides for 8 to 10 minutes, then remove and set aside.
04 - Add chopped onion, carrots, and celery to the same pot. Sauté until softened, about 5 minutes. Add minced garlic and cook for an additional minute.
05 - Stir in tomato paste and cook for 2 minutes to develop flavor.
06 - Pour in the red wine, scraping the bottom of the pot to release browned bits. Simmer for 3 minutes to reduce slightly.
07 - Return lamb shanks to the pot. Add stock, rosemary, thyme, and bay leaves. Bring mixture to a gentle simmer on the stovetop.
08 - Cover the pot and transfer to the preheated oven. Cook for 2 to 2½ hours, until lamb is tender and easily pulls from the bone.
09 - Remove lamb shanks and cover to keep warm. Simmer sauce over medium heat for 10 to 15 minutes to thicken, if desired.
10 - Discard herb sprigs and bay leaves. Adjust seasoning to taste. Serve lamb shanks with the sauce spooned over the top.