Finally found some time to thicken the apple sauce. Poured the jar of very runny sauce into a microwave dish approximately twice the size, gradually heated it to boiling point or thereabouts, stiring every 30 seconds. Then another 3 minutes stiring every 30 seconds as it started to become thicker.
Interestingly the taste is tangier and more to my liking. The Microwave is still in one piece as there was never a chance of an explosion
25% of my apple sauce has disappeared as steam which surprised me