I was chatting to a chef at Tandoori Lane in Fulham about 6 years ago, asking him why/how many of the curries have such an incredible smokey flavour, yet not too overpowering. Back then I thought it was from the chicken or lamb tikka imparting their flavour from the tandoor, or maybe smoked paprika, but he told me something quite different, something I'm yet to try but think I will give a go since it popped back into my head a few days back...
He said that it was mainly house special dishes he used it in, but that many BIR's use this method to achieve the flavour.
Apparently they fry lots of garlic in oil until it's browning. They then take out the garlic (with a slotted spoon I imagine) and drop a few hot coals from the tandoor into the oil. How long the coals stay in the oil, I have no idea. I do remember him saying "we use just a little, just a little, it's powerful" meaning the resultant oil I guess.
Apologies if this method has already been posted.