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Brown glazed crock of French onion soup topped with toasted baguette and melted, browned cheese dripping over the rim, with sliced baguette, whole onions and fresh thyme behind it

Vegetarian French Onion Soup

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Slowly caramelized onions simmered in a rich, savory vegetable broth with thyme and a splash of white wine, ladled into bowls and broiled under toasted baguette and bubbling Gruyère-style cheese. The French bistro classic, made without beef broth.
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Prep Time 15 minutes
Cook Time 1 hour 15 minutes
Total Time 1 hour 30 minutes
Servings: 4 servings
Course: Soup
Cuisine: French
Ingredients Method Notes

Ingredients
  

For the soup
  • 3 tablespoons butter
  • 1 tablespoon olive oil
  • 3 pounds yellow onions about 5 large, halved and thinly sliced
  • 1 teaspoon salt plus more to taste
  • 1/2 teaspoon sugar
  • 3 cloves garlic minced
  • 2 tablespoons all-purpose flour
  • 1/2 cup dry white wine or see notes for a substitute
  • 6 cups vegetable broth
  • 1 tablespoon soy sauce
  • 4 sprigs fresh thyme or 1 teaspoon dried thyme
  • 1 bay leaf
  • 1/4 teaspoon black pepper
  • 2 teaspoons balsamic vinegar
For the cheese toasts
  • 8 slices baguette about 1/2 inch thick
  • 1 1/2 cups shredded Gruyère-style cheese about 6 ounces

Method
 

  1. Melt the butter with the olive oil in a large Dutch oven or heavy pot over medium heat. Add the onions and salt and stir to coat. Cook for 15 minutes, stirring every few minutes, until the onions are soft and have collapsed.
  2. Stir in the sugar and lower the heat to medium-low. Keep cooking for 30 to 35 minutes more, stirring more often toward the end and scraping up the browned bits from the bottom of the pot, until the onions are deep golden brown and jammy. If they start to stick or scorch, stir in a tablespoon of water.
  3. Add the garlic and cook for 1 minute. Sprinkle in the flour and stir for 1 minute. Pour in the wine, scrape the bottom of the pot, and simmer for about 2 minutes, until it has mostly cooked off.
  4. Add the broth, soy sauce, thyme, bay leaf and pepper. Bring to a boil, then lower the heat and simmer, partly covered, for 20 minutes. Remove the thyme stems and bay leaf and stir in the balsamic vinegar. Taste and add more salt if needed.
  5. While the soup simmers, heat the broiler with a rack about 6 inches from the heat. Arrange the baguette slices on a baking sheet and toast for 1 to 2 minutes per side, until golden.
  6. Set 4 oven-safe bowls on a rimmed baking sheet and ladle in the soup. Float 2 toasts on each bowl and cover them with the cheese. Broil for 2 to 3 minutes, watching closely, until the cheese is melted, bubbling and browned in spots.
  7. Let the bowls stand for a couple of minutes before serving, since they will be very hot.

Notes

Take your time with the onions: The deep flavor of this soup comes from slow caramelizing, so do not rush that step with high heat. A wide pot helps the onions brown instead of steam.
Broth: Choose a dark, full-flavored vegetable broth or a mushroom broth. A pale, sweet carrot-heavy broth will make the soup taste flat.
No wine: Use an extra 1/2 cup of broth and increase the balsamic vinegar to 1 tablespoon.
Cheese note: Traditional Gruyère is made with animal rennet. If that matters to you, look for a Swiss-style or Gruyère-style cheese labeled vegetarian.
No oven-safe bowls: Top the toasts with the cheese and broil them on the baking sheet, then float them on the soup.
Make it vegan: Use olive oil or vegan butter and a vegan cheese that melts well.
Make ahead: The soup, without the toasts, keeps in the refrigerator for up to 4 days and freezes well for up to 3 months. Reheat and add the cheese toasts just before serving.

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