To create your madras powder combine black peppercorns, cassia, cloves, coriander, fenugreek, mustard, poppy, cumin and fennel seeds, and grind to a fine powder with an electric grinder, blender, or pestle and mortar.
Stir in the turmeric and 1 tsp of Kashmiri chilli powder into the spice blend.
Place the lamb in a large bowl and rub with 2 or 3 tablespoons of madras curry powder and the salt until all the meat is coated. Transfer the remaining powder into a well-sealed jar for another time.
Heat the oil in a large cast iron pan until hot. Add the mustard seeds – once they start to pop, stir in the curry leaves and then the onions.
Soften the onions until they turn dark brown (about 20 minutes) before adding the green chilli and ginger along with the finely chopped garlic.
Keep stirring as the mix has a tendency to catch on the bottom of the pan. If it does catch add a splash of water.
After a few minutes, add the tomatoes, tamarind and if you like it very spicy add a tsp of hot red chilli powder. Bring this to the boil then reduce the heat and simmer to create a thick masala sauce.
Once it is shiny and thick add the lamb to the pan. Stir to coat the meat with the sauce. Reduce the heat to the lowest setting, cover and leave to cook very gently for 40 minutes to 1 hour, until it's cooked through.
Stir occasionally until the sauce has thickened and the lamb is tender.