Vinegar: 1/2 tbs ( or you can use lemon juice)
In a pan add 2 tbs of oil , fry the grated coconut until it turns it color to golden brown. Once it become fried, off the flame and allow it to cool.Using a mixer make a thick paste grated coconut.
In a bowl add chicken pieces, add 1 tbs of ginger paste , 1 tbs of garlic paste, 1 tbs of salt, 1tbs red chili powder, 1/2 tbs turmeric powder, 1/2 tbs of pepper powder and 1/2 tbs of vinegar into it. Marinate the chicken with ingredients and keep aside for at least 1 hours.
In a pan add 4 tbs of oil, once oil become hot add remaining ginger, garlic paste, 1 stem of curry leaves , and green chilies into it. Saute it and add chopped onion into it. Add one tbs of salt now and stir it well.once it onions turn it color to golden brown add chopped tomatoes into it. Mix it and cook the tomatoes. Add required amount of water( based on gravy, 1/2 or 1 cup ) into it. After 10 minutes add chicken pieces into it. cook for 10 minutes. After this add potato pieces into it stir it well. Then add 1 tbs of red chili powder, 1/2 tbs of turmeric powder, 1 tbs of pepper powder, 1 tbs of Coriander powder and 2 tbs of chicken masala power. Stir it well and cook for 10 minutes( cook the chicken well). After 10 minutes add coconut paste and cook for 15 to 20 minutes. Once it is cooked well and started bubbling add coriander and mint leaves.
Tip: you can avoid chicken masala powder, instead of that increase the quantity of other powder by 1/4 spoon.