Hi Phil,
I work in a IR here in Australia one day a week and prepare the gravies on that day that are used for the rest of the week.
We cook our base gravies for approx 2-3 hours. Once they are cooked they go into a fridge and are used as required.
When a dish is being made for a customer, the gravy is taken from the fridge and added to the pot at the appropriate time with the other ingredients.
The onion cooking part of the gravy making process takes a good 2 hours, this you might find interesting, no water is added to the onions while cooking. They slowly cook and caramelize for the two hours along with a couple of whole spices and the smell is absolutely amazing while cooking and nothing like the boiled approach. Oh and another surprise, no such thing as mix powder either!
Again this is a major difference to BIR, the chef said he would never boil onions for a gravy though, so different techniques are out there but these curries are amazing and I can reproduce them at home.
My advice, if you can, get into a restaurant either working part time, or see if you can get part time lessons in a restaurant.
There are a few others on the site who have been able to get into restaurants as well and it is where you pick things up properly, can ask questions etc.
While the above process works for me to be able to recreate the curries at home, it may not work for you in that you are looking to re-create tastes from your local restaurant and their processes/mixes will be different.
Unfortunately we all have preconceived notions of what dishes are supposed to be. I remember there was a lot of surprise when the Ashoka Rogan Josh gravy revealed that it had coconut and I think almonds in it, and how could Rogan Josh have that in it. Here in Aus, most of them do, others don't so to one person what is Rogan Josh is completely different to what others know as Rogan Josh. How about this Rogan Josh descriptionn from one restaurant close to my place...
Rogan Josh - $16.90
Chef's special creation. Chicken is simmered with lentils, with the added flavours of Cardamom and fresh garlic. A spicy exotic curry of the Kashmiri style.
I've never seen/read/experienced lentils in a Rogan Josh, but this place does it and that's their version.
In any case, if you can get into a restaurant to work/take lessons, then at least you can order a dish from that place taste it, get the chef to teach you how to make it and then reproduce at home. It may taste completely different from the dish from your local, but you will have learnt that dish from their perspective.
Cheers,
Mark