Note: Slice your onions thin. It makes the texture of the soup far more enjoyable.
Clean and slice your onions.
In a soup pot, sauté your onions in the olive oil until they are soft and dark brown with caramelization.
Add beef broth and vinegar to the pot and boil until the liquid has cooked down by approximately half.
Serve sprinkled with approximately 2 tbsp. parmesan cheese sprinkled over the top.
If you want croutons, you can make a few whole grain croutons at home. See link above.
Please note that the nutrition data below is a ballpark figure. Exact data is not possible. Data does not include optional ingredients.