French onion soup is a classic dish invented in the Les Halles market in Paris. Late at night (or early in the morning, depending on how you look at it) workers would need a hearty dish to help them stay full for the hours of work ahead of them. Cheap and filling, the recipe below fit the bill.
The secret to a good French onion soup is to caramelize the onions well before adding the broth. The best French onion soups are made with homemade beef broth, which you can prepare by purchasing soup bones from a butcher and simmering them low and slow for several hours. If you don't have time for that, a good-quality store-bought broth will work fine.