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French Onion Soup with Gruyere and Baguette

French onion soup with slowly caramelized onions simmered in rich beef broth, finished under the broiler with a bubbly golden Gruyere topping. This bistro-style version includes toasted baguette and a savory, wine-scraped flavor base.
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Prep Time 25 minutes
Cook Time 1 hour 25 minutes
Total Time 1 hour 50 minutes
Servings: 6 servings
Course: Dinner
Cuisine: French
Calories: 650
Ingredients Equipment Method Notes

Ingredients
  

Onion base
  • 4 tbsp unsalted butter
  • 1 tbsp olive oil
  • 3 lb yellow onions thinly sliced About 6 large onions
  • 1 tsp salt
  • 1 tsp granulated sugar
  • 3 garlic cloves minced
  • 1 tsp Worcestershire sauce Worcestershire sauce
  • 1 tsp black pepper Use 1/2 tsp black pepper as listed in source
  • 2 tbsp all-purpose flour
  • 1 tsp fresh thyme 2 sprigs, thyme leaves/stems removed later
  • 1 bay leaf
  • 1 tbsp Worcestershire sauce Use 1 tbsp Worcestershire sauce as listed in source
  • 1 tsp black pepper Use 1/2 tsp black pepper as listed in source
Broth and toppings
  • 1 cup dry white wine Use 1/2 cup
  • 6 cup beef broth Use 6 cups (1.4 L)
  • 6 baguette slices toasted 1 inch thick slices
  • 2 cup shredded Gruyere cheese Use 2 cups
  • 0.5 cup grated Parmesan cheese Use 1/2 cup (50 g)

Equipment

  • 1 Dutch oven
  • 1 sheet pan

Method
 

Caramelize the onions
  1. Melt the butter with the olive oil in a large Dutch oven over medium heat. Stir until the butter melts and the surface looks glossy.
  2. Add the onions and salt, cover, and cook for 15 minutes over medium heat, stirring occasionally, until softened. The onions should turn translucent at the edges.
  3. Uncover and stir in the sugar, then cook over medium-low heat for 30 to 45 minutes more, stirring often, until deep golden brown and jammy. Scrape the bottom as needed so browned spots don’t burn.
  4. Stir in the garlic and cook for 1 minute over medium-low heat. Keep it moving so it smells fragrant but doesn’t brown too much.
Build the soup
  1. Pour in the white wine and scrape up the browned bits, then cook until almost evaporated. You should see the liquid reduce noticeably and look thicker.
  2. Sprinkle in the flour and stir for 1 minute until it’s fully incorporated. The mixture should look smooth and slightly sandy.
  3. Add the beef broth, thyme, bay leaf, Worcestershire sauce, and black pepper, then bring to a boil. Once boiling, reduce to a simmer and cook for 25 minutes.
  4. Remove the thyme stems and bay leaf, then adjust the salt to taste. The broth should taste balanced and savory.
Broil and finish
  1. Preheat the broiler and set 6 oven-safe bowls on a sheet pan. Line up the bowls so they fit under the broiler easily.
  2. Ladle the soup into the bowls and top each with a toasted baguette slice. Aim for full coverage so the crust sits on top of the soup.
  3. Cover the baguette with Gruyere and Parmesan, then broil for 3 to 4 minutes until melted, bubbly, and browned in spots. Watch closely so the cheese browns without burning.

Notes

For best caramelization, keep the heat at medium-low after adding sugar and stir often so the onions become jammy without scorching. Store leftover soup in the fridge up to 4 days; reheat gently on the stove and add fresh toasted bread and cheese before serving (freezing is not recommended because the onions and cheese topping texture can change). For a lighter option, use low-sodium beef broth and reduce added salt to taste.