- 10 medium yellow onions (about 4 1/2 pounds) , halved, peeled, and thinly sliced
- 2 tablespoons olive oil
- 2 tablespoons sugar
- 1 teaspoon dried thyme
- Coarse salt and ground pepper
- 3 cans (14 1/2 ounces each) reduced-sodium chicken broth
- 3/4 cup dry red wine
- FOR CHEESE TOAST (OPTIONAL)
- 4 slices toasted multigrain bread
- 4 ounces sliced Swiss cheese
- Preheat oven to 450 degrees. In a large roasting pan, toss together onions, oil, sugar, thyme, 2 teaspoons salt, and 1/4 teaspoon pepper. Cover tightly with foil; cook until steamed, about 30 minutes. Uncover; cook, stirring every 30 minutes, until onions are golden brown and caramelized, 1 to 1 1/4 hours more.
- Transfer onion mixture to a large saucepan (reserve roasting pan); stir in broth and 6 cups water. Bring to a boil; reduce heat to a simmer. Cook until liquid has darkened, about 20 minutes.
- Meanwhile, deglaze the roasting pan with wine: Place the pan over medium heat; add wine. Scrape bottom of pan with a wooden spoon or scraper to loosen any browned bits. Simmer until reduced and syrupy, about 2 minutes. Pour liquid (and browned bits) into soup. Season with salt and pepper. (If freezing, let cool completely before transferring to airtight containers, leaving 1 inch at top.)
- If desired, make the cheese toast: Heat broiler. Place bread on a baking sheet; top with Swiss cheese. Broil until cheese is bubbly and golden brown, 2 to 3 minutes. Cut each slice into four triangles.
- To serve, divide soup among bowls; garnish each with two triangles of cheese toast, if desired.