Traditional recipes for caramelized onions will instruct you to cook the onions over low heat for about 45 minutes. I am way too impatient for that. Since I use the onions to top steaks, burgers, and livers, I really don't need them super-caramelized and evenly cooked. It's OK if they're mostly soft and golden, with parts of them browned and caramelized. So in my version, I only cook them for 10 minutes over medium heat. If you want a traditional result - super soft, sticky, and evenly browned - you should cook them for 45 minutes over low heat, stirring frequently.