Cooking onions for a base (advice please)

[Secret Santa]

My plan is to strip things back to basics and get every part just as it should be.

Stop frying them then and just boil them like the BIRs do.

[emin-j]

I recently made the 4kg Glasgow base as posted by bigboaby1 and to achieve the 'milky' state of the onions took over three hours of boiling  this needed frequent adding of water to prevent the onions from burning and sticking to the bottom of the cooking pot . The addition of all the extra water did not seem to lessen the flavour of the base and would guess it is only water that is boiling off.
The finished base was creamy sweet and rich , the Madras and Korma curry's I made with the base were excellent.