Each chef has his own recipe and little tricks that make his gravy different from someone else's which they keep close to their chests, this is probaly due to the fact that if the restaurant owner finds out how to make it they would get replaced by someone cheaper, maybe.
Unfortunately that just backs my assertion that there could be a secret ingredient in the base sauce. There's just no winning with this one. We'll go round and round with guesses and suppositions because we just don't know!
I think its all about technique and practice rather than any secret ingredient
I definitely think this is wrong. The techniques used in the final curry preparation have been witnessed and verified by at least four people in this group at different establishments. It seems to boil down to:
1.very high heat from start to finish (not normally reproducable at home as the curry house gas rings put out at least five times the BTU as the largest ring on a domestic gas hob). If you're using an electric hob you've got no chance of reproducing the required heat.
2.loads of oil, possibly of the spiced variety from the top of the base sauce, or from the frier
3.browning the garlic/ginger adequately
4.two or three small ladles of base sauce with at least one of these reduced to almost dry consistency
5.igniting the oil/sauce during the final cooking (I briefly got a look in two kitchens many years ago and I saw this in both)
6.pre-cooking anything that can't be cooked in about 10 mins, which is the average final cooking time for the finished curry
Did I miss anything there?
The point is, of all the things we know the techniques of the final curry preparation are the best known because they have been witnessed and confirmed by several people. Therefore I doubt that technique is the missing factor, assuming of course that we are all capable of faithfully reproducing this technique each time.
So if we've got the techniques right, and we've got the base sauce right, and we have people who have recipes for the final curries witnessed at restaurants, but still cannot reproduce the missing aroma/flavour of the takeaway curry, what's left?