I love this soup because it is a meal in itself and so, so cozy. It takes a little time, but the aroma in your house will be amazing — and the sourdough croutons under all that melted Gruyère are what winter evenings were made for. (A loaf a day or two past fresh is perfect here.)
- 3 tablespoons unsalted butter, cut into 3 pieces
- 6 large yellow onions (about 4 pounds), halved and cut pole to pole into ¼-inch-thick slices
- Table salt
- 2 cups water, plus extra for deglazing
- ½ cup dry sherry
- 4 cups low-sodium chicken broth
- 2 cups beef broth
- 6 sprigs fresh thyme, tied with kitchen twine
- 1 bay leaf
- Ground black pepper
- 1–3 slices rustic sourdough, cut into ½-inch slices, then cut to fit your crocks
- 8 ounces shredded Gruyère cheese (about 2½ cups)
Directions for the chef
Adjust an oven rack to the lower-middle position and heat the oven to 400°F. Generously spray the inside of a heavy-bottomed large Dutch oven (at least 7 quarts) with nonstick cooking spray. Place the butter in the pot and add the onions and 1 teaspoon salt. Cook, covered, for 1 hour — the onions will be moist and slightly reduced in volume.
Remove the pot from the oven and place it over medium heat. Cook the onions, stirring frequently and scraping the bottom and sides of the pot, until the liquid evaporates and the onions brown, reducing the heat to medium if they're browning too quickly. Continue to cook slowly, stirring frequently, until the onions are golden brown. Stir in ¼ cup water, scraping the pot bottom to loosen the crust, and cook until the water evaporates and the pot bottom has formed another crust, 6 to 8 minutes. Repeat this deglazing process 2 or 3 more times, until the onions are very dark brown. Stir in the sherry and cook, stirring frequently, until it evaporates, about 5 minutes.
Stir in the broths, 2 cups water, thyme, bay leaf, and ½ teaspoon salt, scraping up any final bits of browned crust. Increase the heat to high and bring to a simmer. Reduce the heat to low, cover, and simmer 30 minutes. Discard the herbs, then season with salt and pepper.
While the soup simmers, arrange the sourdough slices in a single layer on a baking sheet and bake in the 400°F oven until dry, crisp, and golden at the edges, about 10 minutes. Set aside.
To serve: adjust an oven rack 6 inches from the broiler element and heat the broiler. Set individual broiler-safe crocks on a baking sheet and fill each with about 1¾ cups soup. Top each bowl with a single layer of sourdough and sprinkle evenly with Gruyère. Broil until the cheese is melted and bubbly around the edges, 3 to 5 minutes. Let cool 5 minutes before serving.
Jan's notes: Sweet onions like Vidalia or Walla Walla will make this overly sweet. Be patient when caramelizing — that's where the flavor lives. Use broiler-safe crocks and keep the rims 4 to 5 inches from the element for a proper gratinée. If using ordinary soup bowls, sprinkle the toasted bread with Gruyère, broil until melted, then float them on top.
For the best flavor, make the soup a day or two in advance. The onions can be prepared, cooled in the pot, and refrigerated for up to 3 days before proceeding.