I was always taught when cooking Indian dishes to fry spices in a chopped/pureed onion and garlic mixture to release their flavour and essential oils.
I was also taught that when the oil separates from the mixture, the spices are done and you can carry on with the next stage of the dish.
That's the principle technique I've always used.
Can someone please explain why the oil separates and what this signifies? Have the spices absorbed as much of the oil as they can and release the rest?
I'd really like to understand this process.