Classic French Onion Recipe

French onion soup lives or dies on one step: how long you let the onions cook before anything else happens. Real caramelization, the kind that turns onions a deep amber brown and jammy-soft, takes 45 to 60 minutes over low heat. There’s no shortcut that gets the same depth of flavor. Everything after that, the stock, the sherry, the broiled gruyère on top, is really just building around what those slow-cooked onions already gave you.

Quick Facts

• Prep time: 15 minutes
• Cook time: 1 hour 30 minutes (about 1 hour caramelizing onions, 30 minutes simmering)
• Total time: 1 hour 45 minutes
• Yield: 4 servings
• Category: Soup
• Cuisine: French
• Calories: ~600 per serving (estimated)

Why This French Onion Soup Works

• Low, slow caramelization for close to an hour converts the onions’ natural sugars into deep color and sweetness that high heat just burns instead of builds.
• Deglazing with sherry lifts the browned fond stuck to the bottom of the pot, which is concentrated flavor that would otherwise stay stuck there.
• A small amount of flour thickens the broth slightly, giving it body without needing a separate roux.
• Toasting the baguette before it goes on the soup keeps it from dissolving the second it hits the hot broth.

Ingredients

• 3 tbsp (42g) unsalted butter
• 1 tbsp (15ml) olive oil
• 3 lb (1.4kg) yellow onions, thinly sliced (about 6 large onions)
• 1 tsp kosher salt
• 1/2 tsp sugar (helps browning)
• 2 cloves garlic, minced
• 1/4 cup (60ml) dry sherry
• 2 tbsp (16g) all-purpose flour
• 6 cups (1.4L) beef stock
• 2 sprigs fresh thyme (or 1/2 tsp dried)
• 1 bay leaf
• Salt and black pepper, to taste
• 1 baguette, sliced into 1-inch rounds, toasted
• 8 oz (225g) gruyère cheese, grated

Equipment

A heavy-bottomed Dutch oven or wide, heavy pot. A thin pot scorches the onions before they caramelize evenly. Oven-safe crocks or bowls for broiling the cheese on top.

Substitutions

• Yellow onions → sweet onions (Vidalia), which caramelize faster and give a sweeter, less complex flavor.
• Beef stock → vegetable stock for a vegetarian version. It loses some depth, so add a splash of soy sauce or a spoonful of miso for umami.
• Gruyère → Swiss cheese for a milder flavor, or a mix of provolone and parmesan.
• Sherry → dry white wine, or skip the alcohol and add a splash of sherry vinegar with the stock instead.

Step-by-Step Instructions

1. Start the onions. Melt the butter with the olive oil in a Dutch oven over medium heat. Add the sliced onions and salt, and cook, stirring occasionally, for 10 minutes until they soften.

2. Caramelize. Reduce the heat to medium-low and add the sugar. Cook, stirring every 5 to 10 minutes and scraping up the browned bits each time, for 45 to 60 minutes until the onions are deep amber brown and jammy, with no crunch left.
3. Add aromatics. Stir in the garlic and cook 1 minute until fragrant.
4. Deglaze. Pour in the sherry, scraping up the browned bits from the bottom of the pot. Cook 2 minutes until mostly evaporated.
5. Add flour. Sprinkle the flour over the onions, stir to coat, and cook 2 minutes to cook out the raw flour taste.
6. Simmer. Add the beef stock, thyme, and bay leaf. Bring to a simmer, then reduce the heat and simmer uncovered for 30 minutes. Remove the thyme stems and bay leaf, and season with salt and pepper.

7. Broil. Preheat the broiler. Ladle the soup into oven-safe bowls, top each with a toasted baguette slice, and pile grated gruyère on top. Broil 2 to 3 minutes until the cheese is melted, bubbly, and browned in spots. Watch closely, since broilers vary and cheese can go from browned to burnt in seconds.

Tips

• Don’t rush the caramelization. If the onions are browning unevenly or smell sharp instead of sweet, the heat is too high, not too low.
• Scrape the bottom of the pot every time you stir the onions. That browned fond is flavor, and it burns if it sits too long between stirs.
• Toast the baguette slices until they’re dry and firm all the way through, not just lightly golden. A soft center turns to mush on contact with hot broth.

Common Mistakes

• Onions taste bitter or burnt: heat too high → lower the heat and give the onions the full 45 to 60 minutes; there’s no way to speed this up without scorching.
• Soup tastes flat: stock wasn’t deglazed thoroughly or the simmer was cut short → scrape up all the fond and let the soup simmer the full 30 minutes to concentrate flavor.
• Cheese doesn’t brown or bubble: bowls too far from the broiler element → move the oven rack up, and use crocks that fit close under the broiler.
• Bread turns to mush instantly: baguette not toasted enough before going on the soup → toast until dry and firm, not just warmed.

Storage

Refrigerate the soup base (without bread or cheese) in an airtight container up to 5 days.

Freezing

Freezes well for up to 3 months, but only the soup base. Freeze before adding bread and cheese, then thaw in the fridge overnight.

Reheating

Reheat the soup on the stovetop until hot, then assemble the toasted bread and cheese fresh and broil just before serving. Bread that’s refrigerated or frozen on top of the soup turns soggy.

Variations

• Red wine version: swap the sherry for dry red wine for a deeper, more savory broth.
• Extra rich: stir a splash of heavy cream into the finished soup for a lighter-colored, creamier version.
• Individual gratinée: instead of floating one large baguette slice, top each bowl with several smaller toasted rounds fully covered in cheese for more crisp edges per bite.

What to Serve With It

A simple green salad, a crusty baguette on the side, or as a starter before a roast chicken or steak dinner.

FAQ

Why do my onions taste bitter or burnt instead of sweet in this French onion soup? They were likely cooked too hot, too fast. Real caramelization needs low, steady heat over close to an hour, not a quick high-heat sauté.

Can I make french onion soup ahead of time? Yes. The soup base keeps well in the fridge and often tastes even better the next day. Add the toasted bread and cheese fresh right before serving.

Do I need oven-safe bowls to make this? Yes, if you’re broiling the cheese directly on top of the soup. If you don’t have oven-safe crocks, melt the cheese over the toast separately on a sheet pan under the broiler, then float it on the soup.

Can I caramelize the onions in a slow cooker? Yes, but it takes 8 to 10 hours on low to reach the same color and flavor a stovetop gets in about an hour.

What can I use instead of alcohol in this French onion soup recipe? Skip the sherry and add a splash of sherry vinegar or apple cider vinegar along with the stock for acidity.

Classic French Onion Soup

Onions caramelized low and slow for an hour, simmered in beef stock with sherry and thyme, then topped with toasted baguette and broiled gruyère.

Print Recipe Pin Recipe

Prep Time 15 minutes mins

Cook Time 30 minutes mins

Total Time 45 minutes mins

Servings: 4 PEOPLE

Course: Soup

Cuisine: French

Calories: 600

Ingredients Equipment Method Notes

Ingredients

  

• – 3 tbsp 42g unsalted butter
• – 1 tbsp 15ml olive oil
• – 3 lb 1.4kg yellow onions, thinly sliced
• – 1 tsp kosher salt
• – 1/2 tsp sugar
• – 2 cloves garlic minced
• – 1/4 cup 60ml dry sherry
• – 2 tbsp 16g all-purpose flour
• – 6 cups 1.4L beef stock
• – 2 sprigs fresh thyme or 1/2 tsp dried
• – 1 bay leaf
• – Salt and black pepper to taste
• – 1 baguette sliced into 1-inch rounds, toasted
• – 8 oz 225g gruyère cheese, grated

Equipment

• 1 Dutch oven
• 1 oven safe soup crocks

Method

 

1. Cook onions with butter, oil, and salt over medium heat 10 min until softened.
2. Reduce heat to medium-low, add sugar, cook 45-60 min, stirring every 5-10 min, until deep amber and jammy.
3. Add garlic, cook 1 min.
4. Deglaze with sherry, cook 2 min.
5. Add flour, cook 2 min.
6. Add stock, thyme, bay leaf; simmer uncovered 30 min. Season, remove thyme and bay leaf.
7. Ladle into oven-safe bowls, top with toasted baguette and gruyère, broil 2-3 min until bubbly and browned.

Notes

 Soup base freezes well; bread and cheese should always be added fresh.