Place a muslin cloth in a sieve suspended over a bowl
Pour the yoghurt onto to the cloth and leave overnight
Reserve the solids and discard the liquid
In a bowl, combine the hung yoghurt, chilli powder, black salt and salt, lime juice, ginger and garlic paste, garam masala, fenugreek leaves and mustard oil in a mixing bowl
Rub over the chicken, then cover and marinate in the fridge for at least 1 hr
For the gravy, put the tomatoes in a deep pan along with the salt, 1 tbsp chilli powder, bay leaves, cardamom, mace, cumin, ginger and garlic
Add 200ml water and cook for 10-15 mins until the tomatoes have broken down
Leave to cool a little, then blend in a food processor until smooth
Strain through a sieve to remove any seeds or tomato skins
In a separate pan, combine the butter, garlic and ginger paste, green chillies and 2 tbsp water