Coat a medium non-stick skillet with a thin layer of olive oil, and sauté the onions over a medium flame, stirring very infrequently. Once they soften and begin to brown on each side, return the flame to low and allow to slowly caramelize. During this time, it is important to make sure the onions are spread as evenly as possible across the pan. Every few minutes, scrape the bottom and redistribute the onions so each gains the maximum amount of surface area. The intention is to slowly crisp the onions by enticing the remaining liquids to sweat out, and for the onions to sweeten by condensing in their own juices. If you stir too often, the onions will turn to mush. This process takes about 20 minutes. This can also be done up to a week in advance and kept in the fridge.