Combine the soaked dried red chilies, garlic, ginger, cumin seeds, black peppercorns, cloves, cinnamon stick, and malt vinegar in a blender. Blend until a smooth paste forms, adding a splash of water if needed.

Place the lamb chunks in a bowl and rub the spice paste evenly over the meat. Cover and let marinate at room temperature for 30 minutes, or refrigerate for longer if preferred.

Heat 2 tablespoons of oil in a heavy-bottomed pot over medium heat. Add the marinated lamb in batches and sear until browned on all sides. Remove the lamb and set aside.

Add the remaining oil to the same pot. Add the sliced onions and cook over medium heat, stirring frequently, until they turn deeply golden brown.

Stir in the chopped tomatoes, red chili powder, and salt. Cook until the tomatoes break down and blend into a thick paste.

Return the browned lamb and any resting juices to the pot. Pour in the water and bring to a boil, then reduce the heat to low, cover, and simmer for 45 to 50 minutes, stirring occasionally, until the lamb is tender and reaches an internal temperature of 74°C / 165°F at the thickest piece.