I absolutely love to cook some of my traditional dishes in a cast-iron pan, and many people say that food tastes so good cooked this way. I have to agree. Use only salt to wash the pan and take care good of it.
This is a two-step dish. Marinating the chicken helps to season it and keep it moist. Then adding it to the masala intensifies and makes it special. I recommend getting a block of tamarind and using fresh instead of the bottled paste, which is too concentrated and just too potent. You can even add the tamarind masala sauce to the yogurt mixture, marinate overnight and grill the chicken the next day.
To make the marinade, combine all the marinade ingredients in a large mixing bowl. Mix well. Add the chicken to the bowl, turn to coat, cover and let marinate in the refrigerator for at least 3 hours or overnight (overnight is best).
To make the sauce, toast the coriander seeds, cumin seeds, peppercorns, fenugreek seeds and whole red chiles in a skillet over low heat until you smell the spices, about 1 minute. Do not let the spices burn. Turn off the heat, add the sesame seeds to the hot pan and stir for a minute or two. Transfer to a blender along with the tamarind pulp and blend to a very smooth paste. Don’t add any water.
Add the oil to a heavy-bottomed cast-iron skillet or kadai and let it get hot over high heat. Add the chicken with the marinade mix. Let it sear and cook and one side. After about 2 minutes, turn the chicken and sear it for another 3 minutes. Then add the pearl onions and toss and brown them. Add the sauce, ketchup, tomato paste and salt, cover the pan and cook the chicken over medium heat for 20 minutes until it is fork tender. Open and check if the chicken is completely cooked. Then uncover the pan and let it dry down until all the sauce sticks to the chicken, tossing occasionally. Serve garnished with some chopped cilantro and a drizzle of lemon juice, with rice or naan.