There is no shortage of recipes for French Onion Soup. Probably every French cookbook includes a recipe and any food blog that tends to the classics...or technique...or French food...will likely have posted a recipe. So I'm really not posting anything new or unusual with this recipe...just a record of the soup that I made and enjoyed and will be teaching...my preferred version in the midst of a world of countless variations.
Throughout all the variations runs one main thread of agreement: a good result with this soup depends upon deep caramelization of the onions. Don't shortcut this step. Recipes differ on how to reach this point, but the goal is the same—soft, sweet, amber-colored onions. A few recipes will begin over higher heat, caramelizing the onions right off the bat and then reducing the heat and allowing the onions to soften. I prefer to start the onions in a covered pot over moderate or moderately low heat. This encourages the onions to release a lot of liquid. They will then begin to stew and soften in their own juices. The collapsed onions are then allowed to cook uncovered until their liquid has evaporated and they are deeply caramelized.
The whole process takes over an hour, but for most of that time they only need to be checked (and stirred) occasionally. It is only towards the end that they need to be watched carefully—and stirred regularly—so they won't burn. The lower the heat and the longer they are cooked, the sweeter they will be.
One major variation among recipes is the type of liquid used. You will find recipes that use a light chicken stock, some that use a rich beef broth and a few that use water. It is actually the recipes that use water that are the most traditional. In its origins, this is a soup of the poor...it would not have been enriched with a meat broth. Madeleine Kamman writes that during the 19th century this simple soup became a specialty of the bistros and cafés of the central market of Paris. I'm not sure when it went from being a water-based to a broth-based soup. Madeleine's version is water-based. I prefer to use a mix of chicken stock and water. Some stock adds a bit of depth—using all stock seems too rich.
As for the other liquids, the soup usually includes white wine...occasionally red. Most of the time the wine is added and reduced before the water or broth is added, but I have seen recipes where the wine is added at the end. Many soups also include Sherry or Port. Gordon Hamersley suggests that Sherry is the appropriate choice with Chicken Stock and Port with Beef...but you should use whichever fortified wine you prefer...no matter what liquid you are using.
The crowning glory of French Onion soup is a slice or two of stale baguette and a bit of cheese. The use of stale bread would have originally been a move of economy...but its inclusion serves to make a light broth-y soup more substantial. At the same time it provides a resting place for the cheese. If you don't have a stale baguette (or other sturdy country-style loaf), toast the bread to dry it out a bit. For a little added richness, give the bread a smear of butter before floating it on the soup.
As far as the cheese is concerned, use a light hand. The temptation to pile it on is great, but the result of too much cheese is a soup topped with a thick, nearly impenetrable raft. Getting this concoction to the mouth without some loss of dignity is difficult. Once there, chewing through such a wad of goo is unpleasant at best and a choking hazard at worst. About an ounce (1/3 cup, coarsely grated) is plenty for a serving of soup. And since you will be using such a restrained hand with the cheese, purchase the best you can afford. A nice, imported, cave-aged Gruyère is perfect. Not only is the flavor better, the melted texture is not as impossibly stretchy as with cheaper cheeses.
If you have only sampled restaurant versions of French Onion Soup, I encourage you to try making it for yourself. Choose a chilly, gray Saturday or Sunday afternoon...when you will be at home and can keep an occasional eye on the stove. Your results will be vastly superior to what you would be likely to get if you went out. And I predict you will be surprised at how flavorful...and filling...such a simple soup can be.
French Onion Soup
(Soupe à l'Oignon Gratinée)
3 T. unsalted butter, divided
2 lbs. yellow onions—peeled, trimmed, halved, cored and thinly sliced lengthwise
1 clove garlic, peeled, trimmed and thinly sliced
1 bay leaf
1/2 T. picked fresh thyme
Freshly ground pepper
3/4 c. dry white wine
5 c. chicken stock
4 c. water
1/3 to 1/2 c. dry sherry (or Port)
6 to 12 slices (3/8- to 1/2-inch thick) baguette or other sturdy, country-style bread (you want the bread to just cover the width of your serving bowls)
6 oz. grated Gruyère cheese (don't skimp on quality—choose a nice, cave-aged cheese...preferably an import)
Melt 2 tablespoons of the butter in a 5-quart Dutch oven (or other large, heavy pot) over moderate to moderately low heat. Add the onions, along with a generous pinch of salt, and toss to coat in the butter. Cover the pot and cook, stirring occasionally, until the onions have collapsed and released their liquid. This will take about 15 to 20 minutes.
Uncover and continue to cook, stirring occasionally, until the onions have shrunk dramatically in volume and have acquired a deep amber color—about 40 to 60 minutes. As the onions begin to color, reduce the heat and use a flat wooden spoon to scrape the bottom of the pan as you stir to release the caramelizing bits. The longer you cook the onions, the softer and sweeter they will become.
When the onions have reached the desired color, increase the heat to medium and add the remaining tablespoon of butter along with the garlic, thyme, bay and a generous grinding of pepper. Cook until the garlic is fragrant and the onions have begun to sizzle a bit in the added butter—about 2 to 3 minutes. Add the wine, increase the heat, and reduce (carefully scraping up all the caramelized bits) completely.
Add the stock, water and sherry and bring to a simmer.
Cook, maintaining a gentle simmer, for about 45 minutes to allow the flavors to blend. Taste and correct the seasoning with salt & pepper (remembering that the Gruyère cheese will be salty).
While the soup simmers, toast the slices of bread (they should be dry—if you are using stale bread, there is no need to toast it). If you like, spread the slices of bread with a bit of butter.
When ready to serve the soup, preheat the broiler (if you have a choice of settings, choose the highest setting) and adjust the oven rack so the top of the soup bowls will be about 4 to 6 inches away from the heat source. Set six oven/broiler proof bowls on a sturdy baking sheet. Ladle the soup into the bowls, being sure to maintain a nice balance of solids and broth in each bowl. Float a slice or two of the bread (covering the surface of the liquid as much as possible without any overlap) in each bowl. Top the bread with an ounce of the cheese, spreading over the surface in an even thickness. Slide the soup bowls under the broiler and broil until the cheese is melted, bubbling and golden brown in spots. Allow the soup to cool for a minute or two before serving—warning your guests that the bowls will be very hot.
(My version of this classic recipe was inspired by many different sources, but it would be fair to say that it draws most heavily on the recipes in Bistro Cooking at Home by Gordon Hamersley and The Balthazar Cookbook by Keith McNally, Riad Nasr & Lee Hanson)