Wash and soak chicken in buttermilk overnight and refrigerate. Drain off the buttermilk fully, the next morning.This is done only to tenderize the chicken. If you have meat tenderizer you can use it too. You can skip this step totally and just marinate with the marination ingredients and set aside for 45 minutes to 1 hour
Make a fine paste of the coriander leaves and green chili, set aside till we use it for seasoning. Coarsely crush or pulse onion in a mixer.
Mix all the marination ingredients along with crushed onions and chicken. If your chicken is not soaked in buttermilk for atleast few hours, then i suggest you set aside after marination for 45 minutes to 1 hour
Cook chicken on a medium flame till tender and soft. If needed you can sprinkle little water. If the chicken oozes out more moisture, evaporate by cooking on high. But do not overcook at high temperature for long. It can make the chicken hard.
Heat a pan with oil, add cumin, when they begin to splutter add curry leaves and green chilies. Fry till the leaves turn crisp
Transfer the cooked chicken and add ground coriander chilli paste.
Mix well and fry for about 3 to 5 minutes on a medium flame, till you begin to get a nice aroma of the coriander leaves.