...I would like to get to grips with a authentic BIR balti paste...
LC, I don't know if you've visted the
Cook4One website. It's been mentioned here before and I believe it's run by a former forum member.
It's chokkablok with world recipes. There is an Indian section, but there is also a separate BIR section in which he has a
Balti Paste recipe on the site which I made a good while back - I can't really remember what it was it was like, only that it was OK (bearing in mind that I've never tasted an 'authentic' Balti). But, at that time, I was flitting from one recipe or technique to another, trying out everything and anything, so being 'OK' is actually something of a recommendation!

There's a lot of good stuff on there.
EDIT: I had a quick search and, lo and behold, I found
my reference to the Balti Paste.