Patience pays. The essence of an onion soup is, well, the onions. When onions are slow-cooked, they break down, releasing their sugars and juices and then they caramelize. What begins as a crisp white onion evolves into a slippery, squishy, mahogany-colored mound of onion – and this is a very good thing. Combined with stock, herbs, wine and a splash of cognac, the amorphous mound of slow-cooked onions becomes the base and richness for a sweet, deep, flavorful soup. Topped with a thick slice of grilled pain paysan which in turn is topped with melted, bubbling alpine cheese, you have a sublime, satisfying and substantial winter soup.
So, here is where patience pays: It is essential that the onions cook for a long time. There are recipes for onion soup where the onions are fried on the cooktop and browned in less than one hour. While they may look like they are close to the desired outcome in flavor, they are not. The onions must sweat, break down, release their juices. The juices, in turn, must slowly evaporate, allowing the onions to caramelize. If you skip this process, you will miss in the soup an extra depth of flavor and body that will leave you struggling to improvise as you desperately rummage through your spice cabinet for that extra something that is missing.
Do not be deterred by the time required; all you need is some advance planning and an oven. While the stovetop works, it does require constant checking and care which is labor intensive for the busy cook. With the oven, the onions can cook through the afternoon, and an hour before dinner the soup is ready to finish. Simplicity, economy of ingredients, time and care – this is the essence of slow cooking, resulting in a rustic, comforting meal that feeds the soul and palate.
French Onion Soup au Gratin
4 tablespoons unsalted butter
5 large yellow onions, about 3 pounds, halved and thinly sliced
1 teaspoon salt
1/2 cup dry white wine, divided
1/2 cup sherry or Calvados brandy
5 cups beef stock or a combination of beef and chicken stock
4 thyme sprigs, tied with kitchen string
1 bay leaf
Salt and freshly ground black pepper
12-15 baguette slices, cut 3/4 inch thick
1 cup grated alpine cheese such as Grùyere, Comté or Emmenthaler
Preheat oven to 400 F. (200 C.) Melt butter over medium heat in a large Dutch oven or heavy oven-proof pot with lid. Add onions and salt. Cook, stirring, 5 minutes. Cover pot and place in oven for one hour.
Remove pot, stir onions and any collected brown bits on sides and bottom of pot. Cover, leaving slightly ajar and return pot to oven. Cook until onions are soft and golden brown, two hours, checking and stirring up browned bits after one hour. (There will be a lot of liquid in the pot at this point.)
Remove pot from oven and remove lid. Transfer to stovetop. Simmer over medium heat until liquid evaporates and onions turn brown, stirring and scraping up any browned bits on bottom and sides of pot, about 20 minutes. Continue cooking to allow a crust to form on the bottom of the pan without burning, about 5 minutes. Add 1/4 cup white wine to deglaze pan and loosen crust. Continue cooking until wine evaporates and another crust begins to form. Deglaze a second time with remaining 1/4 cup wine. The onions should be dark brown at this point. Add sherry, and cook stirring until sherry evaporates. Add stock, thyme and bay leaf. Stir and scrape up any brown bits on bottom and sides of pot. Bring to a boil, reduce heat and simmer, covered, 30 minutes. Discard thyme and bay leaf. Season with salt and pepper to taste.
Make the croutons:
While the soup simmers, lightly brush bread slices with olive oil. Place on a baking sheet and bake in 400 F. (200 C.) oven until light golden and crisp, 5-8 minutes. Remove and set aside.
Finish the soup:
Divide soup evenly among 4 oven-proof bowls or crocks arranged on a baking sheet. Gently lay croutons in one layer to cover most of the surface. Sprinkle cheese evenly over crouton and soup. Place baking sheet in oven under grill element. Broil until cheese is bubbling and golden brown, 2-3 minutes. Remove from oven and serve immediately.