Soupe a l’oignon gratinée is not a difficult recipe, but you can’t cut corners. In a recipe with few ingredients such as this soup, it’s essentially that all must be of the best possible quality. For best results, follow three key steps. First, give the onions a careful, slow cooking to properly caramelize. Second, steep and simmer them in a beef or chicken stock that itself is rich with flavor. The best option: Make your own stock.
If you used store-bought store, be sure to check the sodium content – your mileage will vary. Avoid bouillon cubes; the result can be unpleasantly salty. Below you’ll find a terrific video lesson from my partner Rouxbe.com on how to caramelize onions.
Lastly, top it off with a quality cheese. Classically, that’s Swiss gruyere or French comté. If neither are available or both too pricey, try a sweet but slightly salty yellow cheese, such as Fontina, Jarlsberg or Provolone. For an even gratin, arrange a rack about six inches from the top broiler in your oven. Be sure to use bowls that can stand up under a broiler or the whole exercise may end in tears.
Note: To make a bouquet garni, tie the herbs together with kitchen string. In a pinch, those wire strips that come with garbage bags or unwaxed dental floss can be employed. For easy clean-up, put the bowls on a cookie sheets lined with foil, parchment or a silpat. Serves four.
1 lb. large yellow onions, sliced thin
1/2 teaspoon salt
1 tablespoon unsalted butter or olive oil
2 tablespoons flour
1 bouquet garni (thyme, parsley sprigs tied together)
1 bay leaf
1/2 cup dry white wine, dry vermouth or champagne
1 tablespoon Cognac (optional)
Two quarts brown stock or best quality packaged broth, boiled
¼ French baguette, sliced thin
6 oz swiss cheese, grated
1 oz Parmesan cheese, grated
Preheat the oven to 350˚F. In a heavy saucepan over high heat, melt the butter or oil. Add the onions and stir to coat with the butter or oil, then cover for about five minutes. This will help to draw some of the moisture out from the onions. Then, uncover, add the salt and turn the heat to low. Continue to cook the onions, stirring occasionally, until the onions are medium-brown and caramelized, about 30 minutes.Sprinkle the top of the onions with the flour and stir thoroughly to coat. Add the wine and Cognac. Once the alcohol has evaporated slightly, add the hot stock. Reduce heat, add bouquet garni and simmer for one hour uncovered.
Meanwhile, toast the baguette slices. Just before serving, top one side of the bread slices with cheese and broil lightly until cheese slightly melts. Remove bouquet garni and ladle soup into four broiler-safe bowls, such as heavy crockware.
Taste the soup, adding more salt if needed. Put the toasts into the soup, cheese side down. Top the soup and bread with a layer of gruyere, topping off with a bit of Parmesan. Bake for 15 minutes, and then put under a broiler for a couple of minutes until the cheese bubbles and browns.