You are right Pete, it must be an ingredient or technique! I have to say that I am convinced that re-using the oil gives that certain "aroma" in my kitchen. The combination of oils from loads of different curries made and mixed together.
I am pretty disgusted with the Bengal, they take your money and then don't care. Having said that my curries from there did not have the taste at all either, so, it's quite obvious to me that they were not in the same league as a good BIR!
I must see if I can get into another restaurant kitchen in the near future. How about you?