For the Malaysian curry powder, toast all of the spices, except the turmeric, in a dry frying pan, for 30 seconds-1 minute, or until they become fragrant. Set aside to cool slightly.
Grind the toasted spices and turmeric to a powder using a pestle and mortar.
For the Malay korma, heat one tablespoon of the oil in a lidded wok, add the lamb, in batches if necessary, and stir-fry for 2-3 minutes, or until browned all over. Remove the lamb from the wok and set aside.
Heat the remaining oil in the wok used to cook the lamb and fry the onion, ginger, garlic, 1 ½ tablespoons of the Malaysian curry powder and all of the chilli powder for 1-2 minutes, or until fragrant (NB: Do not let the mixture burn).
Add the reserved lamb to the wok and season to taste, with salt. Stir until well combined. Stir in the saffron strands and soaking water, cashew nut paste, cinnamon stick, then pour in enough water to cover the lamb by 2.5cm/1in. Bring the mixture to the boil, then reduce the heat, cover the wok with the lid and simmer, stirring occasionally, for 1¼-1½ hours. (You may need to add more water if the mixture begins to dry out.)
Stir in the yoghurt and tomatoes and return the mixture to a simmer for 1-2 minutes.
To serve, spoon the rice into each of 4 serving bowls, top each bowl with some lamb curry and garnish with the coriander leaves.