SERVES 6
Tie the parsley and thyme sprigs together with kitchen twine so they will be easy to retrieve from the soup pot. Use broiler-safe crocks and keep the rims of the bowls 4 to 5 inches from the heating element to obtain a proper gratinée of melted, bubbly cheese. If using ordinary soup bowls, top the toasted bread slices with the cheeses as directed in step 3 and return them to the broiler until the cheese melts, then float them on top of the soup.
SOUP |
|
2 |
tablespoons unsalted butter |
3 |
pounds red onions (about 6 medium), halved pole to pole and sliced crosswise ⅛ inch thick |
Table salt |
|
6 |
cups low-sodium chicken broth |
1¾ |
cups beef broth |
¼ |
cup dry red wine |
2 |
sprigs fresh parsley (see note) |
1 |
sprig fresh thyme (see note) |
1 |
bay leaf |
1 |
tablespoon balsamic vinegar |
Ground black pepper |
|
CHEESE CROUTONS |
|
1 |
small baguette, cut on the bias into ½-inch slices |
4½ |
ounces thinly sliced Swiss cheese |
1½ |
ounces Asiago cheese, grated (about ¾ cup) |
1. FOR THE SOUP: Melt the butter in a large Dutch oven over medium-high heat. Add the onions and ½ teaspoon salt and cook, stirring frequently, until the onions are reduced and syrupy and the inside of the pot is coated with a deep brown crust, 30 to 35 minutes. Add the chicken and beef broths, red wine, parsley, thyme, and bay leaf, scraping the pot bottom with a wooden spoon to loosen the browned bits, and bring to a simmer. Simmer to blend the flavors, about 20 minutes; discard the herbs. Stir in the balsamic vinegar and season with salt and pepper to taste. (The cooled soup can be refrigerated in an airtight container for up to 2 days; return to a simmer before finishing the soup with the croutons and cheese.)
2. FOR THE CROUTONS: Adjust an oven rack to the upper-middle position and heat the oven to 350 degrees. Arrange the baguette slices on a rimmed baking sheet and bake, turning once, until lightly browned, about 15 minutes. Remove the bread from the oven, carefully adjust an oven rack 6 inches from the broiler element, and heat the broiler.
3. Set individual broiler-safe crocks on the baking sheet and fill each with about 1½ cups of the soup. Top each bowl with two baguette slices and divide the Swiss cheese slices, placing them in a single layer, if possible, on the bread; sprinkle with 2 tablespoons of the grated Asiago and broil until the cheese is browned and bubbly around the edges, 7 to 10 minutes. Cool for 5 minutes; serve.