Hi ELW,
The gravies are being added in chef spoon amounts.
One dish for example might have 2 chef spoon of onion gravy and 0.5 chef spoon of butter gravy, along with a couple of other spices or ingredients. Another might have 1 chef spoon onion gravy, 1 chef spoon korma gravy, 0.25 chef spoon vindaloo paste.
Vindaloo is the simplest, it is just the vindaloo paste, pre-cooked meat with a little stock, and then water added. Let cook and reduce back down. Others might involve frying some mustard seeds, curry leaves, chili then adding the onion paste followed by meat & stock, hot water, and then coconut milk etc.
Boiling/hot water is added to the dish which turns the pastes into gravy, then it is reduced down to the desired consistency.
Cheers,
Mark