Wash chicken pieces, keep them in a plastic colander. This straining process removes the excess water from chicken.

Peel the potatoes. Cut them horizontally into equal halves, wash and keep aside.

Heat 4 tbsp oil in a deep frying pan/kadai. Add half amount of thinly sliced onions with a pinch of salt (adding a pinch of salt speeds up the browning process). Using a spatula, fry the onions continuously over medium heat. Add the whole garlic cloves in between. Mix and keep frying until all the onion slices have reached a dark, rich brown colour. Remove from the pan and keep aside to cool. 

In a large bowl marinate the chicken pieces with fried onion-garlic, kashmiri mirch powder, lemon juice, and garam masala powder. Keep aside for 1 hour.

Now heat 8-9 tbsp oil in the same deep frying pan. Fry the potatoes, let them turn golden brown, remove and keep aside.

In the remaining oil add bay leaf, dry red chilli, and green cardamoms. Stir for a few seconds, add rest of the sliced onions, fry until light brown in colour. 

Add the ginger-garlic paste, cumin powder, coriander powder, turmeric powder, and chopped tomatoes. Mix well and mash the tomatoes with the help of the spatula. Cook the masala over medium heat until it starts leaving the oil (1-2 minutes approximately).

Add marinated chicken pieces and green chillies, mix well, cover, and cook over low heat. Uncover and keep stirring in between. 

When the chicken is half cooked add salt, black peppercorn powder, potatoes, and sugar. Mix, cover and cook until the chicken is fully done.

Serve hot Chicken Kosha with roti, luchi, parota, puri, kochuri, pulao or fried rice whatever you like. This Chicken Curry goes well with almost every Indian style rice dishes.