Forgot to add, I've tried various nuts, cashews ground and in butter form (like peanut butter but cashew), ground almond meal, ground pistachio. I also bought a small container of both Asafoetida and Amchoor, grasping at straws for a mystery ingredient.
One of the closest things I came across was a dish called a Mango Puliserry, to which I added chicken, but again not quite right.
Another thing is that it seems to be chicken prepared either as a mild Tikka or Tandoori or possibly just pre-cooked before going into the gravy. When you ask they just nod and say yes.
One store in Newcastle actually has a little market next door and when I asked in there I was told, Mango pulp, coconut milk and a little Garam Masala. I knew without trying that this was not even near the right thing. They just wont tell.
I've been trying to make variations of this dish for the best part of 10 years, and on some days have had my kitchen littered with dozens of experimental samples. No prize yet.