I've been to the Brisbane cooking classes described by Mark. He's actually setting up his own website but not sure if it's open to the public yet - Mark will advise.
Anyway as Mark says the secret is in the gravy which is more like a paste. Also the chicken needs to be precooked, and the dish is quickly assembled from the gravy and the chicken and is diluted to the desired consistency.
Aha, I've found Mark's original thread here:
https://curry-recipes.co.uk/curry/index.php?topic=8382.0Also I posted some photos on that thread, you can adapt that to making Australian Style butter chicken as well, I was doing a Madras a the time.
With a butter chicken I don't use blended cashew nuts, I use ground almonds which are easier and about the same price, Mark says the restaurants use either, or a combination, depending on what's available. Couple of heaped table spoons does the trick.