Its nearly the same way as i do our base sauce - except i probably boil it a bit quicker
I put in the onions and bits of veg with oil and start the boil down in its own juices really, with a spoon of salt after about 20 mins of stirring the stuff in, the onions are all transparent etc etc then goes in the boiling water and spices and cook for another 40 mins
liquidise then ready to use... how ever i very rarely use it straight away i let it go cold then reheat it even a couple of times then use it
best, Rich