Slice onions and put them in a pan over medium heat.
Drizzle with vegetable oil, then toss to coat. Cover the onions with a lid and cook for 10 minutes.
Stir the onions, replace the lid and let them continue to caramelize for another 10 minutes.
Stir and continue cooking for another 5 minutes, when golden brown and soft.
Oil - Don't use more than 2 tablespoons of oil or butter, or the sautéed onions can become too greasy. Be sure to put a lid on the sauté pan - this speeds up the cooking and helps the onions retain their moisture.
Make them Vegan - To make the onions vegan, use a plant based oil or butter.
Refrigerate - Once the onions are cooked, let them cool to room temperature and place them in an airtight container in the fridge and they will keep up to 7 days. You can then use them as is in recipes, or you can reheat them gently on the stovetop to serve.
Freeze - Store in airtight container or freezer bag up to 3 months. Double wrap to avoid onion odor seeping into other frozen goods.