To caramelize onions, heat 2 tablespoons olive oil over medium heat until hot, add slices onions, cover pan, and let saute for about 3 minutes with stirring. Continue to saute oven medium heat, stirring occasionally until onions begin to brown. Reduce heat to medium-low and continue to slowly saute, stirring about once a minute until the onions are soft and brown. This process can take up to 45 minutes depending on desired darkness of onions.