01 - Pat the lamb shanks thoroughly dry with paper towels and season generously on all sides with salt and pepper.
02 - In a large heavy-based pot or Dutch oven, heat the vegetable oil over medium-high heat. Sear the lamb shanks on all sides until deeply browned, approximately 3-4 minutes per side. Remove and set aside on a plate.
03 - In the same pot, add the sliced onions and sauté until golden brown and caramelized, about 10 minutes. Stir occasionally to prevent burning.
04 - Add the minced garlic and grated ginger to the pot. Cook for 1-2 minutes, stirring constantly until fragrant but not browned.
05 - Stir in all ground spices (coriander, cumin, garam masala, turmeric, chili powder, black pepper) along with whole spices (bay leaves, cloves, cardamom pods, cinnamon stick). Toast for 1 minute, stirring constantly to release their essential oils.
06 - Add the canned chopped tomatoes to the pot and cook for 5 minutes, allowing them to break down and release their juices into the spice mixture.
07 - Return the seared lamb shanks to the pot. Pour in the lamb or beef stock and bring the mixture to a gentle simmer.
08 - Cover the pot with a tight-fitting lid, reduce heat to low, and cook gently for 2.5 hours. Turn the shanks occasionally to ensure even cooking.
09 - Stir in the plain yogurt, fresh chopped tomatoes, and sliced green chili. Simmer uncovered for another 45-60 minutes, until the lamb is fork-tender and the sauce has thickened considerably.
10 - Skim any excess fat from the surface if desired. Adjust seasoning with additional salt to taste.
11 - Garnish generously with fresh chopped cilantro and serve immediately with lemon wedges on the side.