George, you didn't give any clue as to what you believe goes into a recipe that has potential. Naming restaurants over there has no benefit on a globally read forum. I'd be happy to try your time consuming procedure if you'd care to provide details.
I read on here years/decades ago that the distinctive flavour comes from browned garlic. I think someone else said highly cooked chillis. I then had the thought that almost everything needs to be roasted so that's what I did and it worked very well. So I started by baking the onions, garlic, peppers and carrots in the oven to make my normal (markJ) base sauce. After all, recipes for roast chicken gravy often say to use a tray of roasted vegetables. All the spices I used were roasted as much as possible, then ground if needed. I used spiced oil with roasted ingredients, also. At the end, I added a classic tarka of browned garlic. I tried lemon, lime and tamarind as souring elements. My favourite is lime, closely followed by lemon. I really don't like tamarind and doubt it's hardly ever used by BIRs. Adding smoke makes it even better. A bottle of 'liquid smoke' was awful. Real smoke was better.
As for lentils, I suggest 100% red lentils are fine. Using other types of lentils, or a mixture, didn't improve the flavour at all.
Good luck! I fear you are handicapped if you have never tasted the real thing.