A recipe for classic French onion soup uses at least 2 pounds of onions, broth, seasonings, butter and flour. White or yellow onions are the best option, and since the onions reduce during cooking using a large amount of onions is necessary.
Add 8 cups of broth, 3 tablespoons each of flour and butter, salt, pepper, and other seasonings to taste. After melting the butter in a pot, add in the seasonings and chopped onions, then cook until the onions are caramelized, or soft and browned. Any liquid ingredients, including broth and an optional cup of wine or brandy, and flour can then be added and brought to a boil. Whole herbs, such as bay leaves or thyme, should be removed after the mixture has simmered for 10 minutes to an hour.
To serve, divide the soup into oven-safe bowls. Place a thick slice of toasted bagette or a few croutons on top of the soup, then cover with cheese. Shredded Parmesan and gruyere go well with this recipe. Place the bowls in the oven and bake long enough to melt the cheese and thoroughly heat the bread. Optional fresh garnishes to add afterward include thinly sliced shallots and green onions.