hi guys if you checkout the threads for both Rajver and mouchak gravies and JerryMs comments they both use coconut milk but i never add sugar to the gravy either if you leave the base unblended to cool at room temperature then place in the fridge for 24 hours the sweetness of the onions comes, i recently made a base on sunday cool the put in the fridge until the wednesday there was a thick layer of deep red oil protecting the veg blended adding water as it was quite thick and made 1 of the best vindaloos i have ever cooked. but before everyone kills me LOL i haven't been using the coconut milk as i have adapted the way i cook the base, ie not using the 2 step method of boil/ add tarka. just start the frozen asda diced onion off 1st oil /salt, mix then add the other veg and water and then the spices and then bring to the boil until the veg are soft and easily cut with a spoon.
regards
gary