Remove skin, wash and cut chicken into eight pieces on the bone. Grind ginger and garlic to a fine paste. Blanch tomatoes in boiling water for two to three minutes.
Drain. Peel the tomatoes and puree them in a blender. Dry roast cashewnuts and coarsely grind with a mortar and pestle. Marinate the chicken pieces in ginger-garlic paste, garam masala powder, red chilli powder and salt for an hour.
Heat butter in a kadai. Add the marinated chicken and sauté for two minutes. Add slit green chillies and continue to sauté for a minute. Add tomato puree and half a cup of water and cover and cook on medium heat for fifteen minutes or till almost done.
Add crushed cashewnuts and cover and simmer for three to four minutes or till chicken is tender. Add lemon juice and coriander leaves and cook for a minute or till oil leaves the masala.
Stir in the fresh cream and mix gently. Remove from heat. Place coal on open flame and heat till it becomes red hot.
Remove from heat and put the coal in a small steel bowl, place the bowl over the chicken, pour a tablespoon of warm ghee over the coal. As soon as it begins to smoke, cover the kadai with a lid.
Open the lid after ten minutes, remove bowl with coal and serve hot.