lo Corry,
By cooking process ,I think its the right amount of spices added at the right stage and cooked for the correct length of time ,
I believe certain BIR's will get a distinct taste by using different oils ie mustard oil or ghee and adding extra bits and pieces, butI reckon if the main part of the dish is done right using Garlic Ginger and the main 5 spices ,Coriander,Cumin,Turmeric, chilli powder and maybe Paprika.
I also think the addition of the tomato element is important ,i have tried puree,passata ,ketchup and combinations of all 3 but still cannot get it quite right but sometimes close