The secret is in the cooking, practice, practice practice.
No, it really isn't. Yes, practice and knowledge of the techniques are important but if that were all there was to it I'd still be able to walk down to the high street and pick up a curry with the lush savouriness and delicious aroma of yesteryear but sadly I can't. So if the BIR chefs themselves can't do it there's almost no chance for me (even with 30+ years of total curry cooking experience).
The problem is that some people's BIR curry standards are, and I won't mince words here, rather low and will be based on what they're used to from their local BIR curries.
A case in point is CT's madras which the majority of people on here feel is an ace madras. I recently tried it again with the recommended MDH kashmiri masala and lemon dressing, as opposed to lemon juice and, to be fair, it was certainly more palatable than my first effort. But it still had the same unpleasant background bitterness from the kashmiri chilli and of course lacked any madras chilli heat because the kasmiri is too underpowered in that department. Add to that that it resembles no madras I've ever eaten and we're seeing a huge rift between one person's expectations and experience of BIR curries and another's.
So no Stephen, it really isn't all about practice.