Soak the cashew nuts in plenty of water. Blend the cashew nuts along with 80mls water to a smooth fine paste andset aside.
Blend the garlic and ginger with a splash of water and set aside. In the same blender add the onions and blend to a smooth paste. Set aside.
In a large bowl add the Greek yogurt, half the amount of Kashmiri chilli powder, black pepper and 2 tsps of the garlic ginger paste. Add the chicken and mix well. Leave to marinate for a few hours or overnight preferably.
In a large nonstick sauce pan, heat the oil over a medium flame. Add the cinnamon, cloves, cardamom and dried chillies. Fry for a few seconds and add the onion paste. Fry for 6-8 minutes. Stir well making sure it doesn't stick to the pan. Add the remaining garlic ginger paste and fry for 1 minute as the raw flavours cook through. Add the remaining chilli powder, turmeric and coriander powder. Stir well and fry for a minute.
Now add the tomatoes and fry for 5 minutes as they begin to soften. Add the marinated chicken and see the pieces stirring well for 7-8 minutes.
Add water and season to taste. Simmer over a low heat for 20 minutes with a lid on. Add the cashew paste and stir for 2 minutes. Turn the heat off. Add the fenugreek leaves and serve warm with naan orparatha.