Clean and cut the lamb, unless the butcher is doing it for you or you are buying pre cut lamb. I do not recommend this as the lamb is not properly cut or cleaned and comes from a mix of several animals thereby resulting in irregular cooking. Try not to cut the cubes very large but rather like big dices.
Add the oil in a heavy casserole and heat it till it gets a haze on the top. Add all the whole spices as well as the red chillies.
As soon as you see the spices swell and puff and change colour add the chopped onions and saute until they get a good brown colour.
Add the lamb and seal well turning occasionally so that it browns better.
When the liquid has almost dried up add the powders and the ginger garlic pastes, stir well.
Meanwhile peel and cut the potatoes into large chunks or cut them lengthways into fours.
When the lamb and the masala is well sautéed add salt & enough water or stock to just about cover the lamb, close the pot with a tight lid and simmer.
Check from time to time also ensuring that the sides of the pot are kept clean.
When the lamb is half done add the potatoes, stir and mix them in well, add the tomatoes if you like, cover the pot and simmer.
When the lamb is cooked, check for seasoning again.
Before serving sprinkle some freshly chopped coriander as well as blend some in if you like fresh coriander. This will give the product a huge kick.
Even without the coriander this is a superb product.