Grind the onion, ginger, garlic and green chillies into a smooth paste.
In a pressure cooker, add the paste, chicken and all the remaining ingredients except the ones for tempering and give it a good mix.
Pressure cook for one whistle on high and then leave it on simmer for 15 minutes. Switch off and allow the pressure to go by itself.
Heat ghee, and fry the onions in it till it becomes brown and crisp. Add into the prepared curry.
Serve warm with tandoor rotis!