Slice the onions very thinly. They should be as uniform in size as possible for even cooking.
Heat the oil in a skillet over low heat. (Do not be tempted to turn up the heat!)
Allow the onions to cook slowly over low heat, stirring every five minutes, or more once they begin to brown. Keep this up until the onions reach your desired level of caramelization - it will take anywhere from 45-75 minutes depending on your stove, pan, and how brown you prefer your onions. Have lots of patience and don't turn up the heat!
Craving more veg-friendly recipes? Shop our collection of vegetarian and vegan cookbooks, including our new Vegan Thanksgiving and Vegan Christmas cookbooks!