Whenever i make this recipe, i dont add the pre-cooked chicken, i cook the finished recipe for around 1 hour on a low heat (and not 10 minutes as stated in the recipe) to get that "brown stuff" on the inside of the pan then scrape that back in and do this for about 1 hour.
Then when i make a Madras for 4 people i add a ladle at a time with the heat on high wait for that to sizzle then turn down heat to medium, then add another ladle, once this starts to bubble turn down heat again to low, dont forget to keep scraping that "brown stuff" back into the sauce then add raw/pre-cooked chicken serve when cooked through (about 15 minutes).
Quite taken back by your comment gazman this recipe is very close to a BIR,your probably not cooking it right ;D