First, marinade the chicken with 2 tablespoons of the curry powder and 1 tablespoon water for about 1 hour. Mix the remaining curry powder with the water to form a curry paste.
Heat a deep wok or frying pan with oil, sautee the chopped onions till they're soft. Add the curry leaves before adding the curry paste.
Stir fry the paste till you can smell the fragrance. Add the marinaded chicken.
Toss everything to coat. Add water till you cover 3/4 of the chicken.
Let it come to a bubble. Add the coconut milk, stir and turn the heat down to low. Cover and let it simmer for about 45 mins to an hour.
Add the peeled and quartered potatoes and let it simmer till the potatoes are fork tender. If you see the curry going too dry, add more water and season.
Check doneness of chicken. Taste and season the gravy with salt. Some like it rather dry, others might prefer it more wet. My hubster likes to flood his 'roti' with gravy so we went with more gravy.
Eat with rice, roti or roti jala.