I've tried different methods and variations on both themes: dry frying in oil of the core spices versus the "classic" Kris Dhillon method of wet simmering the spices in the curry base.
After 12 years of trial and error I've come to the conclusion that by far the best approach, in terms of restaurant authenticity, is Kris Dhillon's approach of wet simmering the spices.
Dry frying the spice core in oil gives, for me, too much of an intense and overpowering flavour which is a million miles away from any restaurant meal I've tasted.
I made a Kris Dhillon chicken curry recipe two days ago (still have some in the fridge) and it is clear that it is as close as it is possible to get to a very good restaurant curry - as close as possible for a simple and accessible recipe and even much closer than more complex recipes.
So after 12 years and countless wasted or disappointing trials and errors - including futile searches for authentic supermarket or chilled curry base sauces - I am sticking not just with Kris Dhillon's curry base (with a carrot or two added) but also with her chicken curry recipe.
I do oil fry garlic and ginger (blended) before adding the curry gravy and I do add a decent curry powder (bought from Spice Mountain at Borough Market - also available online).
Sometimes the simplest and original things are the best. Just took me over 12 years to grasp it.