In some dishes, one of the most important ingredients is time. It is long-term quenching distinguishes minced meat with tomatoes from the "Bolognese" sauce, in a short time not to cook a favorite cold, and ideal meringues are obtained only if they are dried for a long time at low temperatures.
So with onion soup, the magic of a long process of steaming and caramelizing gives the onion such a magical taste, aroma and consistency that no other ingredient can claim the leading role in the dish, and will only shade and emphasize the basic taste.
This traditional for cold days thick soup is prepared not hard, but quite a long time. The result is worth the time.