Heat the oil in a medium sized frying pan until the oil just starts to shimmer.
Add the cassia bark. You should see little bubbles forming around it. Cook for about 30 seconds.
Add the onions. Cook the onions until they are fully translucent. If you can get the edges to brown a bit that's a good thing.
Stir in the garlic ginger paste. Gently fry until the garlic ginger paste stops sputtering. This is the only messy step.
Turn your heat down to medium low and add your spice mix and the curry leaves. Cook for about 30 seconds. You really want to fry your spices in the oil. Don't skimp on the oil. Bad things happen if the spices stick and burn.
Add the Indian hotel curry gravy. Stir it really well to get the oil to combine with the curry gravy. You want everything mixed together at this point. Bring to a simmer.
Add the chicken thigh pieces in a single layer. Nestle them down into the sauce. Cover and ccok about 5 minutes. Remove the cover, flip the chicken and recover. Cook until the chicken is done. Use an instant read thermometer if you have one. You are shooting for an internal temperature of 160F. It will get to 170F as the curry finishes cooking.
Add the tamarind paste and coconut milk.
Look at the consistency. If you are happy with it, cover and simmer for 2 minutes. If it's too thick, add a bit of water. If it's too thin don't cover it.
Chettinad chicken curry is great with rice or, if you really want to go large, rice and a paratha. Parathas make everything better...