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Bistro French Onion Soup with Bubbly Gruyere and Sourdough

French onion soup with Gruyere gets its deep flavor from slowly caramelized onions, dry sherry, and beef broth. Toasted sourdough and bubbly, browned cheese finish each broiler-safe bowl.
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Prep Time 15 minutes
Cook Time 1 hour 28 minutes
resting 5 minutes
Total Time 1 hour 48 minutes
Servings: 6 servings
Course: Dinner
Cuisine: French
Calories: 570
Ingredients Equipment Method Notes

Ingredients
  

For the soup
  • 3 tbsp unsalted butter
  • 1 tbsp olive oil
  • 6 yellow onions large, about 3 pounds, thinly sliced
  • 1 tsp kosher salt
  • 0.5 cup dry sherry
  • 8 cup low-sodium beef broth
  • 1 tsp dried thyme
  • 1 bay leaf
  • 1 tsp Worcestershire sauce
  • 0.5 tsp black pepper
For the topping
  • 6 slices sourdough bread cut 1/2 inch thick
  • 12 oz Gruyere cheese shredded

Equipment

  • 1 6-quart Dutch oven
  • 1 baking sheet
  • 1 rimmed baking sheet
  • 6 16-ounce broiler-safe bowls

Method
 

Caramelize the onions
  1. Melt the butter and olive oil in a 6-quart Dutch oven over medium-low heat, then add the onions and salt. Cook uncovered for 50 to 60 minutes, stirring often, until the onions are deeply golden and very soft.
  2. Stir in the sherry, scraping up any browned bits from the bottom of the pot, and cook for 2 to 3 minutes until most of the liquid has evaporated.
Simmer the soup
  1. Add the beef broth, thyme, bay leaf, Worcestershire sauce, and black pepper; bring to a boil, then reduce the heat and simmer uncovered for 25 to 30 minutes.
Toast the bread
  1. While the soup simmers, heat the oven to 400°F and arrange the sourdough slices on a baking sheet. Toast for 8 to 10 minutes, turning once, until crisp and lightly golden.
Broil and serve
  1. Remove the bay leaf and set the oven broiler to high. Ladle the soup into six 16-ounce broiler-safe bowls and arrange them on a rimmed baking sheet.
  2. Top each bowl with a slice of toasted sourdough and divide the Gruyere evenly over the bread. Broil 2 to 4 minutes, 6 to 8 inches from the heat, until the cheese is bubbling and browned in spots.
  3. Let the bowls rest for 5 minutes before serving.

Notes

For the deepest onion flavor, stir often and let the onions turn deeply golden and very soft. Refrigerate leftovers for 3 to 4 days; the soup base freezes well, preferably without the bread and cheese. For a gluten-free option, use gluten-free sourdough.