Transfer the oil from frying the chicken into a clean skillet. This is now spiced oil. You want to get back to 3 tablespoons so if it looks low a little more oil won't hurt.
Heat the oil over medium heat.
Add the black cardamom. You should see little bubbles form. Cook for about 20-30 seconds.
Stir in the garlic ginger paste. Gently fry until the garlic ginger paste stops sputtering. This step can get a bit messy so be ready.
Turn your heat down to medium low and add your spice mix. Cook for about 30 seconds. You want to fry your spices in the oil. There are fat soluble compounds in spices. This is how magic happens.
Add the yoghurt. Stir it well. Fry for about 30 seconds. I know frying yoghurt is a bit strange. Just trust me. The yoghurt needs to get cooked out.
Add the tomato puree and the green chilies. Fry the mixture for 2-3 minutes. You will need to add a bit of water or stock to keep it from getting too thick. But at least when that happens you'll know you're doing it right.
Add the Indian hotel curry gravy. Stir well. You want everything mixed together. Bring to a simmer.
Add the cream and kasoori methi. Stir to combine.
Add the chicken thigh pieces in a single layer. Nestle them down into the sauce. Cover and cook about 5 minutes.
Remove the lid, flip the chicken and replace the lid. Continue simmering until the chicken is done. You are shooting for an internal temperature of 170F. Should only be a couple minutes more.
Chicken changezi should be a saucy curry. Look at it in your pan. It's going to need a little extra liquid (water or no-sodium chicken stock) to get it there. Somewhere between 2-4 tablespoons. You want a consistency just slightly thicker than heavy cream.
Serve garnished with fried shallots if you like. It's not essential but it is a really nice touch.