Heat oil in a thick bottom pan on medium high heat, when the oil is hot fry the potatoes till golden. Remove with slotted spoon, drain and keep aside.
In the same panTemper the same oil with bay leaves, cardamon cinnamon and cloves along with the sugar.
When they start sputtering and the sugar caramelises (this gives nice colour to the curry), add the sliced onions. Fry on low-medium heat till the onion turn golden brown.
Pour in the marinated chicken and fry with the onions on medium heat for 8-10 minutes.
Add the chopped tomatoes and cook, stirring continuously. The chicken will release lot of water.
Add the fried potatoes and cook uncovered on medium for 10-12 minutes until the oil separates from the masala, then and half cup of warm water and mix everything well. Check for the seasoning, add salt and sugar if required. Cover and cook on low heat for another 25-30 minutes.
Finally add the bengali garam masala and green chillies and give it a good mix. If the chicken and the potatoes are cooked then increase the flame and fry the chicken till oil separates.
Garnish with Coriander and serve it with rice and roti or bengali mishti pulao.