Classic French Onion Soup Recipe

Overview

Classic French onion soup depends on one unhurried step: cooking the onions until they are deeply golden, soft, and almost jammy. Give them time over medium to medium-low heat, stirring whenever the bottom of the pot starts to brown.

The finished soup is savory and rich, with a crisp baguette slice and a blanket of melted Gruyère on top. This recipe makes 4 generous servings and uses oven-safe bowls for the final broil.

Ingredients

• 3 tablespoons unsalted butter
• 1 tablespoon extra-virgin olive oil
• 2 pounds yellow onions, about 5 medium onions, thinly sliced from root to stem
• 1 teaspoon kosher salt, plus more to taste
• 2 garlic cloves, finely chopped
• 1/2 cup dry white wine, such as Sauvignon Blanc or Pinot Grigio
• 1 tablespoon all-purpose flour
• 6 cups low-sodium beef broth, preferably warm
• 2 teaspoons Worcestershire sauce
• 1/2 teaspoon dried thyme, or 1 teaspoon fresh thyme leaves
• 1 bay leaf
• 1/4 teaspoon freshly ground black pepper
• 8 slices baguette, about 1/2 inch thick
• 1 1/2 cups finely shredded Gruyère cheese, about 6 ounces

How to make it

1. Prepare the onions. Trim the onion ends, cut the onions in half from root to stem, peel them, and slice them thinly. Uniform slices help them soften at the same rate.

2. Start the onion base. Melt the butter with the olive oil in a large heavy-bottomed pot or Dutch oven over medium heat. Add the onions and salt. Stir to coat, then cook for 10 minutes, stirring every few minutes, until the onions begin to soften and release moisture.

3. Caramelize slowly. Reduce the heat to medium-low and cook for 35 to 50 minutes, stirring every 5 to 8 minutes. Scrape the bottom whenever browned bits appear. The onions are ready when they are very soft, reduced to roughly one-quarter of their original volume, and a deep golden brown. If the bottom darkens before the onions are soft, lower the heat and add 1 tablespoon of water to loosen the browned bits.

4. Add garlic and deglaze. Stir in the garlic and cook for 1 minute, just until fragrant. Pour in the white wine and scrape the bottom of the pot with a wooden spoon. Simmer for 3 to 5 minutes, until the wine is reduced by about half and the sharp alcohol smell has faded.

5. Thicken the broth. Sprinkle the flour over the onions and stir constantly for 1 minute so no dry flour remains. Slowly pour in the beef broth while stirring. Add the Worcestershire sauce, thyme, bay leaf, and black pepper.

6. Simmer the soup. Bring the soup to a gentle simmer, then reduce the heat to low. Cook uncovered for 20 to 25 minutes. The broth should taste savory and the onions should be completely tender. Remove the bay leaf and thyme stems, if using fresh thyme. Taste and add salt only after the broth has simmered.

7. Toast the baguette. While the soup simmers, heat the oven to 400°F. Arrange the baguette slices on a baking sheet and toast for 8 to 10 minutes, turning once, until dry and crisp at the edges. Set the oven to broil when the soup is ready.

8. Assemble carefully. Place 4 oven-safe bowls on a sturdy baking sheet. Ladle the hot soup into the bowls, leaving at least 1 inch of space at the top. Float 2 toasted baguette slices on each serving and divide the Gruyère over them, taking the cheese close to the edges so it melts into a browned lid.

9. Broil the cheese. Broil 4 to 6 inches from the heat for 2 to 4 minutes, watching continuously. The cheese should be fully melted, bubbling, and browned in spots. Carefully transfer the bowls to plates or heatproof trivets and let them stand for 2 minutes before serving; the soup and bowls will be extremely hot.

Expert tips

• Slice consistently: Thin, even slices soften and brown more predictably than thick or irregular pieces.
• Do not rush the onions: High heat can burn the surface while the centers remain firm. Deep golden brown is the goal; blackened bits will make the soup bitter.
• Use the right broth: Regular-sodium broth may work, but taste before adding salt. Vegetable broth can replace beef broth for a meat-free version, though the flavor will be lighter.
• Wine substitution: Replace the white wine with an equal amount of extra broth plus 1 teaspoon of sherry vinegar or lemon juice added at the end of simmering.
• Cheese alternatives: Comté or Emmental melts well in place of Gruyère. A mixture of low-moisture mozzarella and Parmesan works when needed, though it will taste less nutty.
• If the soup tastes flat: Add a small pinch of salt first, then a few drops of Worcestershire sauce or wine vinegar. Add gradually so the broth does not become salty or sharp.
• If the onions are burning: Move the pot off the heat briefly, scrape up any browned fond, and add 1 to 2 tablespoons of water. Resume cooking at a lower temperature. Discard the onions if they taste acrid or strongly burnt.

Serving and storage

Serve the soup immediately after broiling, while the cheese is bubbling and the bread is crisp. A simple green salad or a small serving of Mediterranean orzo salad can balance the richness without competing with the soup.

For make-ahead preparation, cool the soup promptly in a shallow container and refrigerate it in a covered container for up to 3 days. Store the toasted bread separately so it does not become soggy. Reheat the soup in a saucepan over medium heat until steaming throughout, then assemble with fresh toast and cheese and broil as directed.

You can freeze the soup without the bread and cheese for up to 3 months in airtight, freezer-safe containers. Thaw it in the refrigerator, reheat until steaming, and add freshly toasted baguette and cheese before serving.

Frequently asked questions

Can I make French onion soup without white wine?

Yes. Replace the 1/2 cup wine with 1/2 cup beef broth and add 1 teaspoon sherry vinegar or lemon juice near the end of cooking if the soup needs brightness.

How do I know when the onions are caramelized enough?

They should be very soft, reduced to about one-quarter of their starting volume, and deep golden brown throughout. They should smell sweet and savory, not raw or burnt.

Can I use a different cheese than Gruyère?

Comté and Emmental are close substitutes because they melt smoothly. A combination of low-moisture mozzarella and Parmesan also works, although the flavor will be milder and less nutty.

Why did my French onion soup taste bitter?

The onions or browned bits on the pot bottom were likely burned. Deep brown is desirable, but blackened onions create bitterness. Lower the heat, loosen the pot with a little water, and remove any acrid pieces before continuing.

Can I prepare French onion soup ahead of time?

Yes. Cook and refrigerate the soup for up to 3 days, then reheat it and add freshly toasted bread and cheese just before broiling. Store the bread separately to preserve its crispness.

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