Preheat large saucepan on medium heat. Add butter or margarine, gradually stir in onions until they are saturated with butter.
Cover and reduce heat to simmer for about an hour. Remove lid and you'll find that the onions have released their naturally sweet flavor.
Add cream and chicken or beef stock, simmer uncovered until the soup has obtained the thickness and texture you prefer.
For richer soup, use less additional liquid.Season with herbs or salt and pepper as desired.