French Onion Soup Recipe with Deeply Caramelized Onions

French onion soup is a French bistro classic: sweet, slowly browned onions simmered in savory broth and served beneath toasted bread and melted cheese. This version builds flavor patiently in one pot, then finishes each bowl under the broiler for a crisp, bubbling top. Broth, wine, and cheese choices vary by region and household, so the recipe includes practical swaps.

Ingredients

3 lb yellow onions (1.36 kg), peeled, halved, and thinly sliced
3 tbsp unsalted butter (42 g)
1 tbsp olive oil (15 ml)
1 tsp fine salt (6 g), plus more to taste
½ tsp granulated sugar (2 g), optional
2 garlic cloves (6 g), finely minced
2 tbsp all-purpose flour (16 g)
½ cup dry white wine (120 ml), or dry vermouth
8 cups beef broth (1.9 L), preferably low-sodium
2 fresh thyme sprigs (about 2 g), or ½ tsp dried thyme (1 g)
1 bay leaf
½ tsp freshly ground black pepper (1 g)
1 tbsp Worcestershire sauce (15 ml), optional
1 baguette, about 12 oz (340 g), cut into ½-inch (1.3 cm) slices
2½ cups grated Gruyère (about 250 g)

Instructions

Slice the onions and set up. Cut the peeled onions into thin, even half-moons, aiming for slices about ⅛ inch (3 mm) thick. Even slices soften and brown at a similar rate. Grate the cheese, mince the garlic, and measure the remaining ingredients before you begin cooking; the onions need frequent attention early on.
Start the onions. Melt the butter with the olive oil in a large, heavy-bottomed Dutch oven or soup pot over medium heat. Add the onions, salt, and optional sugar. Stir until the onions are coated, then cook for 10 minutes, stirring every couple of minutes, until they have softened and released liquid. If they begin sticking before they soften, lower the heat slightly and scrape the base of the pot.
Caramelize slowly. Reduce the heat to medium-low and cook the onions for 55 minutes, stirring and scraping the bottom every 5 to 7 minutes. As moisture cooks away, the onions will shrink and turn golden, then a deep amber brown. If a dark layer forms on the pot, stir in a tablespoon of water and scrape it up; that browned residue adds flavor, while black, burnt patches taste bitter. Keep the heat moderate rather than rushing this step.
Add garlic and flour. Stir in the garlic and cook for 30 seconds, just until fragrant. Sprinkle the flour over the onions and stir continuously for 1 minute so it coats them evenly and loses its raw taste. The small amount of flour gives the broth a little body; do not expect a thick gravy.
Deglaze, then simmer. Pour in the wine and scrape the pot thoroughly. Let it bubble for 2 minutes, then add the broth, thyme, bay leaf, pepper, and Worcestershire if using. Bring the soup to a gentle simmer, not a hard boil, and cook uncovered for 23 minutes. Remove the thyme stems and bay leaf. Taste the broth and adjust salt and pepper; low-sodium broths differ, so season only after simmering.
Toast the baguette. While the soup simmers, heat the oven to 400°F (200°C). Arrange the baguette slices in one layer on a baking sheet and toast for about 7 minutes, turning once, until dry and lightly golden at the edges. Toasting helps the bread hold its shape under the broth, though it will soften in the middle. Switch the oven to broil when the soup is ready.
Top and broil. Set six oven-safe bowls on a sturdy baking sheet. Ladle in the hot soup, leaving room at the top. Float one or two baguette slices on each bowl, then divide the Gruyère evenly over the bread and toward the edges. Broil about 3 minutes, watching closely, until the cheese is melted, bubbling, and browned in spots. Broilers vary, so do not walk away. Use oven mitts to transfer the bowls, and let them stand for a minute before serving; the bowls and soup will be very hot.

Tips

Give the onions time. Deep color comes from gradual browning, not simply from adding sugar or turning the burner high. A wide, heavy pot gives moisture room to evaporate. If your pot is crowded, stir patiently and allow the onions to cook down rather than increasing the heat until they scorch.
Choose broth thoughtfully. Beef broth gives the classic robust flavor. Low-sodium broth makes it easier to control the final seasoning. For a vegetarian soup, use a full-flavored vegetable broth; the result will be lighter and less beefy, but still savory. Check that the Worcestershire sauce is vegetarian if you use it in that version, or leave it out.
Use a suitable cheese. Gruyère melts smoothly and has a nutty, savory taste. It can be expensive or hard to find; Swiss cheese or Emmental is a practical substitute, with a milder flavor. A little grated Parmesan mixed in adds salty sharpness, but Parmesan alone may not make as stretchy a topping.
Watch the broiler and salt. Cheese can go from browned to burnt quickly, and broth reduces as it simmers. Taste before adding extra salt, especially if using regular-sodium broth, Worcestershire, and salty cheese together.

Serving Suggestions

Serve each bowl as soon as the cheese has browned, while the bread is crisp on top and the soup is hot underneath. French onion soup is filling enough to be a light main course, particularly when each portion gets two slices of bread and a generous blanket of cheese. For a larger meal, serve smaller bowls before roast chicken, a simple steak, or a vegetable tart.

A sharply dressed green salad makes a fresh contrast to the rich broth and cheese. Keep its dressing bright with vinegar or lemon, and serve it alongside rather than putting greens into the soup. A little extra black pepper or thyme at the table is welcome, but additional salt is usually unnecessary. Warn guests that the oven-safe bowls retain heat long after the cheese stops bubbling.

Variations

Alcohol-free: Leave out the wine and deglaze the pot with ½ cup (120 ml) broth. A teaspoon of cider vinegar stirred in at the end can restore some of the wine’s gentle acidity, but add it gradually and taste. The soup will be a little less aromatic, while keeping its onion-and-broth character.

Vegetarian: Replace the beef broth with a deeply flavored vegetable broth and omit Worcestershire unless its label confirms it is vegetarian. Some Worcestershire sauces contain anchovies. If desired, add a small splash of soy sauce for savory depth, then taste before adding salt because soy sauce is salty.

Different cheese or bread: Emmental, Swiss, or a mixture of Gruyère and Parmesan works in place of Gruyère. A country loaf can stand in for baguette; cut it into pieces that fit the bowls and toast until dry. Softer sandwich bread tends to collapse more quickly, so it is a less sturdy choice.

Stovetop bowls: If you do not own oven-safe bowls, broil the cheese on toasted bread on a baking sheet, then place one cheese toast on each bowl of soup. You will miss the classic cheese draped over the bowl’s rim, but avoid transferring hot soup-filled dishes to and from the broiler.

Storage and Reheating

For the best texture, store the soup and toasted bread separately. Cool the soup promptly and refrigerate it within 2 hours of cooking, in a covered container. It keeps for 3 to 4 days in the refrigerator. Do not refrigerate soup with the bread and melted cheese already on top unless necessary; the bread becomes soggy and the cheese firms as it chills.

Reheat only the amount you need in a saucepan over medium heat, stirring occasionally until steaming throughout. USDA FSIS guidance is to reheat leftovers to 165°F (74°C); check the soup with a food thermometer. Add a splash of broth or water if it has thickened. Toast fresh baguette slices, ladle the hot soup into oven-safe bowls, add cheese, and broil as directed.

To freeze, cool the soup without bread or cheese, portion it into freezer-safe containers, and freeze for up to 3 months for best quality. Thaw overnight in the refrigerator, then reheat to 165°F (74°C) before topping with freshly toasted bread and cheese. Freezing can soften the onions slightly, but the flavor remains useful for a quick meal.

Frequently Asked Questions

Why are my onions not turning brown?
They may still be releasing water, the pan may be crowded, or the heat may be too low. Continue cooking uncovered, stir periodically, and give the moisture time to evaporate. If the pot is very full, the onions will soften before they brown. Avoid turning the heat sharply higher, since the bottom can burn before the onions caramelize evenly.

Can I make French onion soup ahead?
Yes. Cook the soup through the simmering step, cool it, and refrigerate it for up to 3 to 4 days. Reheat it to 165°F (74°C), toast the bread, and add the cheese just before serving. Keeping the bread and soup separate preserves the bread’s texture and makes the final broiling step straightforward.

What onions work best?
Yellow onions are a dependable choice because they balance sweetness and savory flavor as they brown. Sweet onions can also work, but the finished soup may taste sweeter. White onions tend to produce a sharper result. Whichever kind you choose, slice them evenly and cook them slowly for the deepest flavor.

Can I make it without wine?
Yes. Use the same amount of broth to loosen the browned bits from the pot. Wine contributes acidity and aroma, so the flavor will be a little rounder without it. If the finished soup tastes too rich, add a small amount of cider vinegar or lemon juice, tasting as you go rather than pouring in a large splash.

Do I have to use oven-safe soup bowls?
No. You can broil the cheese on the baguette slices on a baking sheet and place one cheese toast on each bowl of hot soup. If you do use bowls under the broiler, confirm that they are oven-safe, set them on a baking sheet, and protect your hands when removing them.

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Safety notes: safe minimum internal temperatures from USDA FSIS; raw and undercooked fish guidance from the U.S. FDA. Food safety notes

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