Me too. Thanks, thomashenry.
One thing that keeps throwing me when I try out some of these great suggestions is that the vindaloo from my favourite local is just meat, potato, and finely pureed gravy. I've poked about in it looking for stuff and there are no little chunks of chopped onion or pepper and if there's any chopped garlic I can't see it (though they could be frying garlic puree). I know people on this site have actually seen these things added to the pan in demonstrations, but it would appear my local doesn't approach the dish in this way. Yet it still has the smoky toffee taste.
That's lead me to believe it's possibly there in the base to start with (but as with everything, I'm not sure!).