Soupe a L'oignon
There are times when the distinctions between the carefully laid-out categories of French cooking become murky. The traditional French onion soup, often described on the menus of restaurants in Franch as a gratinee, is a case in point. In some places it's more soup, in others, more gratin-what we call a baked onion casserole. Onion sup is almost always gratineed by slowly baking so that the layers of bread and cheese on top of the broth from a delicious savory crust, but every version is different, some emphasizing bread and cheese more than onions and broth.
5 pounds onions, preferably read
4 tablespoons butter
10 cups beef, turkey, or chicken broth
1 medium size bouquet garni
4 cups 3/4 inch cubes cut from crusty slices of French bread, preferably sourdough.
25 cups finely grated Swiss Gruyere or other full-flavored firm cheese (about 5 pound)
Peel and slice the onions as thin as you can. This is easiest with a plastic vegetable slicer, called Benriner cutter. Melt the butter over medium heat in a wide, heavy bottomed pot large enough to hold the sliced onions. Add the onions and stir every few minutes over medium heat until they soften and release liquid, about 15 minutes. At this point, you can turn the heat to high to reduce the liquid, but keep a close watch and stir every minute or two so that the onions don't scorch. When most of the liquid has evaporated, after 15 minutes, turn the heat back down to medium and keep stirring and scraping the bottom of the pot with a wooden spoon to keep the caramelized juices from burning. When all the liquid has evaporated and the bottom of the pot is coated with a shiny glaze, after 5 to 10 minutes, pour in 1 cup of broth and turn the hat to high. Stir the onions, again scraping off any caramelized juices that cling to the bottom and sides of the pot. when the broth completely evaporates and again forms a brown glaze on the bottom of the pot , add the rest of the broth and the bouquet garni.
Gently simmer the soup for 10 minutes. Be sure to scrape the bottom of the pot so that the caramelized juices dissolve in the soup. Season to taste with salt and pepper. Remove the bouquet garni.
While te onions are cooking, spread the bread cubes on a sheet pan and bake them in a 400 F oven for about 20 minutes, turning them over every few minutes so that they brown evenly. Unless you are making the soup ahead of time, leave the oven on for baking the crocks of soup.
Ladle the hot soup into individual 10 to 12 ounce soup crocks or souffle dishes. Sprinkle half the cheese over the soup and distribute the toasted bread cubes among the crocks. Sprinkle with the remaining cheese. Put the crocks on a sheet pan and bake them at 400F until the cheese bubbles and turns light brown, about 10 minutes. Serve immediately. (You can also assemble the soups earlier in the day and refrigerate them until shortly before serving.