In a wok, fry potatoes with a pinch of salt until golden brown, transfer potatoes to paper towel and set aside.
In same oil, fry sliced onions until crispy golden. Drain oil on a paper towel and spread on a single layer to crisp. Crush onion with hand or in a food processor and mix in marinated chicken.
In same wok, leave only ½ cup oil and (remove extra oil ) cook marinated chicken for 7 minutes until color changes then add tomato puree and cook further for 10-15 until all tomato water dries and oil separates. Your chicken should be tender by now or cook further as needed. Sear chicken ( bhunofy) well for rich taste.
Now add whipped yogurt,and bring gravy to a boil. Now, mix in chat masala (if using) potato, prunes, mint, coriander and green chilles, mix well. Chicken gravy is ready.