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.)