Here is where patience pays off: It's essential that the onions cook for a long time. They must sweat, break down and release their sweet juices.
The juices, in turn, must slowly evaporate, allowing the onions to caramelize.
If you skip this process, you will miss that extra depth of flavor that makes onion soup so satisfying.
Don't be put off by the time required. With this technique, all you need is an oven, with little effort involved until you're ready to finish the soup.
The onions will cook through the afternoon -- filling your house with delicious aromas -- and an hour before dinner, move them to the stovetop to finish, and make the croutons.
This is the essence of slow cooking: Simplicity, economy of ingredients, time and care, resulting in a comforting, warming and deeply gratifying meal.
ONION SOUP AU GRATIN
SERVES: 4 to 5
ACTIVE TIME: 1 hour and 15 minutes
TOTAL TIME: about 4 hours
• 4 tablespoons unsalted margarine
• 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
• 5 cups beef stock (or chicken stock)
• 4 thyme sprigs, tied with kitchen string
• 1 bay leaf
• Salt and freshly ground black pepper, to taste
• 1 baguette, sliced 3/4 inch thick
• Olive oil, to coat bread slices
• 8 ounces coarsely grated (vegan) cheese, or more as needed Preheat the oven to 400 degrees. Melt the margarine in a large Dutch oven or ovenproof pot with lid over medium heat. Add the onions and salt, and cook until soft, 8 to 10 minutes. Cover the pot, transfer to the oven and cook 1 hour.
Remove the pot from the oven and stir the onions and any collected brown bits on sides and bottom of pot. Partially cover the pot and return to the oven. Cook until the onions are soft and golden brown, 1 1/2 to 2 hours, checking and stirring the browned bits after 1 hour. (There will be a lot of liquid in the pot at this point.)
Remove the pot from the oven and transfer to the stovetop. Simmer, uncovered, over medium heat until the liquid evaporates and the onions turn brown, 15 to 20 minutes, stirring and scraping up any browned bits on the bottom and sides of the pot. Continue cooking to allow a crust to form on the bottom of the pan without burning, about 5 more minutes.
Add 1/4 cup white wine to deglaze the pan and loosen the crust. Continue cooking until the wine evaporates and another crust begins to form, 4 to 5 minutes. Deglaze a second time with the remaining 1/4 cup wine. The onions should be dark brown at this point.
Add the sherry and cook, stirring, until the sherry evaporates, 2 to 3 minutes. Add the stock, thyme sprigs and bay leaf. Stir and scrape up any brown bits on the bottom and sides of the pot, and bring the liquid to a boil. Reduce heat to low, cover the pot and simmer for 20 minutes. Discard the thyme and bay leaf and season with salt and pepper to taste.
While the soup simmers, make the croutons. Reheat the oven to 400 degrees. Lightly brush the baguette bread slices with olive oil and arrange on a baking sheet. Bake in the oven until crisp and golden, 6 to 8 minutes.
Divide the soup evenly between 4 to 5 ovenproof bowls or crocks arranged on a baking tray. Gently lay the croutons in one layer over the soup to cover as much of the surface as possible. Sprinkle the cheese evenly over the croutons to cover, adding more cheese if needed. Transfer to the oven and broil until the cheese is bubbling and golden brown, 2 to 3 minutes.
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