To a wide mouthed, heavy bottom cooking pot (dutch oven or heavy wok shaped pot would be great too), add mustard oil and let heat up on medium flame till slightly smoky.
Reduce to low flame and add the whole spices - bay leaves,cinnamon, cloves, green cardamom, black peppercorns and cumin seeds. Let crackle and fry the spices for 8-10 seconds or so taking care not to burn.
Introduce the sliced onions. Bump up the stove to low medium heat. Fry the onions for about 9-12 minutes until nicely golden brown (but not too dark). Avoid stirring too much while onions fry. Tip - Take time to brown the onions. This not only intensifies the flavor and color of the masala but also contributes to its texture, preventing it from becoming overly soft during extended cooking. Add the ginger garlic and cilantro stems next. Add 1-2 tablespoon of water and fry for 10-15 seconds.
Chicken goes in next on medium-high heat. Sprinkle ½ teaspoon salt on the chicken and stirring intermittently, fry it for next 3-4 minutes with onions until you see no pink.
Sprinkle coriander, turmeric and red chili powder. Toss around and fry until the spices coat the chicken. About 1-2 minutes.
Crushed tomatoes go in next along with 1 teaspoon of salt. Combine everything together and in about 1-2 minutes you will see a lot of liquid in the pot. That's what we want, the chicken will cook in its juices and this liquid.
Reduce the heat to low, cover the pot and let cook for 25-35 minutes or until fall apart tender. Adjust time depending on quality and size of the chicken you are using. Keep checking by uncovering the lid and add little water if/as needed.
Uncover, you will see a much thicker and deep colored sauce in the pot now with a thin layer of oil separating. (image 14) Finish the chicken masala with garam masala, kasuri methi and amchur powder
Sprinkle the cilantro leaves(image 16). Rest the curry for 20 minutes(if possible). Serve!