In a small spice grinder or coffee grinder, blend together all the ingredients for the Rogan Josh masala: Black cardamom, green cardamom, cloves, cinnamon, mace, fennel seeds, cumin seeds, ground ginger and the all-important Kashmiri chilli powder. Blend, stopping half way through to ensure all the spices get some blade time. Once finely ground, pass the masala through a sieve to remove any unground spices. You can grind these again, and then add them back into the mix.
To make the rest of the curry:
In a small bowl, mix together the Rogan Josh masala, yoghurt and cornflour (cornstarch). Stir to create a smooth paste.
Heat the ghee in a large, heavy-based pan. Add the asafoetida, garlic and ginger. Sauté for 10-15 seconds but don't let the ingredients brown. Add the mushrooms and 1/4 tsp salt. Cook over a medium heat, moving them around the pan to brown them evenly. If you find the garlic is browning too much, add a small splash of water (about 50ml). Once the mushrooms have softened and browned slightly, remove them from the pan onto a plate.
Add the yoghurt mixture, along with 300ml water. Cook and stir over a medium heat until the mixture comes to the boil, about 6-7 minutes. During this time you can add in the saffron and the remaining 3/4 tsp salt.
Return the mushrooms to pan and add in the black chickpeas. Stir well and bring back to the boil. Cover and simmer over a medium-low heat for 25 minutes. Mix often.
Remove the lid from the pan and simmer for a further 10 minutes uncovered to thicken the curry to your desired consistency. I like to keep mine on the soupier side so I can enjoy it with rice. During this time, you'll notice the oil begins to separate from the curry and float on top. This is the 'rogan' element of Rogan Josh.
Garnish with fresh coriander leaves and serve.
If you don't have a spice grinder, use a pestle and mortar or buy pre-ground spices and simply mix together.This curry tastes even better the next day! Make in advance and refrigerate for up to 3 days. Ensure food is piping hot before serving.