I just bung 2 star anise 3 or 4 bay, some peppercorns and maybe a few cloves and/or cardamoms (last two not essential) into a a big pot with the left-overs of a roast chicken (bones and everything), with a couple of uncooked 'savers' chicken wings. Boil it all for 2 or 3 hours, filter the lot through muslin (from any good cook-shop), into a big pot.
Then I add all the veg that I use for the base, and continue as usual....
I REALLY REALLY suggest anyone who is looking to get another 3% of the way to "the final 5%", to give this a try! Home made chicken stock does not necessarily taste a lot like chicken, particularly in a curry with so many other strong flavours. BUT rather, it seems to act like a general flavour enhancer, it seems to fill-out the flavour in a way that is dificult to discribe, but very effective.
Sorry, I know I've banged-on about this before, and perhaps this is not the thread to mention again; but it IS a very good use for muslin!