01 - Preheat oven to 320°F or prepare slow cooker on low setting. Season lamb shanks thoroughly with salt and black pepper.
02 - Heat olive oil in a heavy-based ovenproof pot over medium-high heat. Sear lamb shanks on all sides until deeply browned, approximately 8 minutes total. Remove and set aside.
03 - Add chopped onions, carrots, and celery to the pot. Cook for 5–7 minutes until softened. Incorporate minced garlic and sauté for an additional minute.
04 - Stir in tomato paste and cook for 1 minute. Pour in red wine and deglaze the pot, scraping up browned bits. Simmer for 2 minutes.
05 - Add crushed tomatoes, stock, rosemary, thyme, bay leaves, and dried oregano. Stir to evenly combine.
06 - Nestle lamb shanks back into the sauce. Bring to a gentle simmer.
07 - Cover pot tightly and transfer to the oven or slow cooker. Cook in the oven for 2.5 to 3 hours, or 7 to 8 hours on low in a slow cooker, until lamb is fork-tender and falling off the bone.
08 - Remove lamb shanks and cover loosely with foil to retain warmth. Skim excess fat from the sauce, then simmer uncovered on the stovetop for 10–15 minutes if a thicker consistency is desired.
09 - Plate lamb shanks and spoon sauce generously over. Garnish with fresh herbs if preferred. Accompany with mashed potatoes, polenta, or crusty bread.