A trick I learned from Seriouseats is that you can use a pressure cooker to carmelize onions in about half an hour. The normal stage of onion cooking where the liquid is still coming out of the onion limits the cooking temperature to about the boiling point of water; by using a pressure cooker, the boiling point of water is raised to the point where browning happens even before the water is gone. See: http://www.seriouseats.com/2016/01/the-food-lab-pressure-coo...