In a recipe with few ingredients such as this one, it’s essential that all must be of the best possible quality. For best results give the onions a careful, slow cooking to properly caramelize, and then simmer them in a broth that itself is rich with flavor. Be sure to use bowls that can stand up under a broiler or the whole exercise may end in tears.
2 medium (1 pound) yellow onions, sliced thin
1 tablespoon unsalted butter
2 tablespoons flour
½ teaspoon dried thyme
1 bay leaf
½ cup (125 ml) dry white wine or dry vermouth
1 tablespoon cognac
2 quarts (2 L) beef stock, boiled
¼ French baguette, sliced thin
6 ounces (180 g) gruyere cheese, grated
1 ounce (30 g) Parmesan cheese, grated (optional)
Preheat oven to 350° F/ 180° C degrees. In a heavy saucepan over medium heat, slowly brown the onions in butter until carmelized. Be patient, this will take at least a half hour. Sprinkle the onions with flour and stir thoroughly. Add the wine and Cognac, cook long enough to evaporate the alcohol and add the hot stock and bouquet garni. 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. Put the toasts into the soup, cheese side down. Top with a layer of Gruyere, and then a bit of Parmesan. Bake for 15 minutes at 350°F / 180° C and then put under a broiler for a couple of minutes until the cheese bubbles and browns. Serves four.