Can anyone tell me how all UK Indian restaurants manage to put that wonderful "smokey" taste into their Tarka Dhals?

Endless recipe books all fail to recreate that elusive smokey taste.? I've read the recipes posted on this site, and sadly they have nothing to add that I haven't tried before.? For the avoidance of doubt, browning garlic just creates a horrible taste but no smokiness.? Browning onion, even to the point of caramelisation, does not create smokiness either.

There is some "trick" known to every UK restaurant that no recipe book writer has ever recorded.? Does anyone out there know the answer, or am I damned to pour fried garlic & onions into my dhal, and live in disappointment?