Many years ago now I saw a couple of TV programmes that showed the addition of very well caramelised onions in to the curry at the end of cooking, but not in the base. One said it was one of the trade secrets. I tried this and felt it definitely improved the curries though still didn't get the old taste I was after. Somehow I stopped doing it, so I'm going to try it again to refresh my memory. The onions have to be cooked with a little sugar for a very long time on a slow heat..about 45 miutes to an hour. At the end they are very soft, very sweet and very brown and savoury. In fact this is how you might cook them for a French onion soup (hint hint Bobby!)