Marinate the chicken in marinade ingredients for at least an hour. The longer the better.
Set a heavy bottomed pan on medium high heat and add a tablespoon of oil to it. If using mustard oil, first heat it to smoke point and let cool. Add the marinated chicken to the hot pan and sear for about 3-4 minutes each side. Take the chicken out in a bowl, cover and set aside.
In the same pan, add remaining 1 tablespoon of oil and add the panch phoren seeds. As the seeds start to splutter, move them to one edge of the pan and add sugar to the other side of the pan and let it caramelize, about a minute. Now add the chopped onions. Add turmeric and a pinch of salt and cook till onions turn light golden, about 7-8 minutes. Scrape any bits of chicken that are sticking to the bottom of the pan and mix them with the onions.
Add the coriander and tomato paste, and cook (bhoono) on medium low heat till you can see tiny droplets of oil appearing on the sides of your masala and all the moisture has evaporated.
While the masala is bhoonoing, cut the chicken into bite size pieces and return to the bowl with all the juices.
Add the chopped chicken to the masala, turn the heat up to medium high, add salt and give everything a big mix. Add about half a cup of water, bring the curry to a boil and reduce heat. Cover the pan and cook until the chicken is done, about 8 minutes. Check and adjust the consistency of the curry by adding more water if you like. If adding more water, bring the curry to a roaring boil again. Check and adjust salt.
Serve hot with chapathi or rice.