Classic French Onion Soup (Gratinée des Halles) – Deeply Caramelized, Comforting, and Cheesy

Few dishes feel as comforting and timeless as Classic French Onion Soup. It’s simple at its core—onions, broth, bread, and cheese—yet somehow it tastes like something far more luxurious. The secret is patience: slowly caramelized onions and a well-developed broth create layers of flavor.

Each spoonful brings sweetness, savoriness, and the irresistible pull of melted cheese. This is bistro food at its best, perfect for a chilly evening or a cozy dinner at home.

What Makes This Recipe So Good

• Deep caramelization: Slowly cooking the onions until they’re a rich, mahogany brown gives the soup its signature sweet-savory depth.
• Balanced broth: A mix of beef stock and a splash of dry wine adds body and complexity without overpowering the onions.
• Classic cheesy top: Gruyère melts beautifully, forming that golden, bubbling crust everyone loves.
• Rustic yet elegant: This soup is budget-friendly and simple to make, but it tastes restaurant-worthy.
• Make-ahead friendly: The flavors only improve after a night in the fridge, making it ideal for planning ahead.

Ingredients

• 3 pounds (1.4 kg) yellow onions, thinly sliced pole-to-pole
• 3 tablespoons unsalted butter
• 1 tablespoon olive oil
• 1 teaspoon kosher salt, plus more to taste
• Freshly ground black pepper
• 1 teaspoon sugar (optional, to help caramelization)
• 2 cloves garlic, minced
• 1 tablespoon all-purpose flour (for slight thickening; optional)
• 1/2 cup dry white wine or dry vermouth (or use dry sherry)
• 6 cups high-quality beef stock (or a mix of 4 cups beef + 2 cups chicken stock)
• 1–2 teaspoons sherry vinegar or red wine vinegar, to finish
• 1 bay leaf
• 3–4 sprigs fresh thyme (or 1/2 teaspoon dried thyme)
• 1 baguette, sliced into 1/2-inch rounds and toasted
• 2 cups grated Gruyère cheese (plus a bit of Emmental or Comté if desired)
• 1/2 cup grated Parmigiano-Reggiano (optional, for extra savory bite)

Instructions

1. Prep the onions: Peel and slice the onions pole-to-pole into thin slices. Keep the slices consistent so they cook evenly.
2. Start the caramelization: In a heavy pot or Dutch oven, melt the butter with the olive oil over medium heat.

   Add the onions, salt, and sugar (if using). Stir to coat.
3. Low and slow: Cook the onions, stirring every few minutes, for 40–55 minutes. Adjust heat to prevent burning.

   You’re aiming for a deep, even brown color and jammy texture.

4. Add garlic and flour: Stir in the garlic and cook 30 seconds. Sprinkle flour over the onions and cook 1 minute more, stirring. This lightly thickens the broth.
5. Deglaze: Pour in the wine.

   Scrape up browned bits from the bottom of the pot. Simmer until the liquid is mostly reduced, 2–3 minutes.

6. Build the soup: Add the stock, bay leaf, and thyme. Bring to a gentle simmer and cook 20–30 minutes.

   Taste and adjust salt and pepper.

7. Finish with acidity: Stir in the vinegar. This brightens the soup and balances the sweetness of the onions.
8. Toast the bread: While the soup simmers, toast baguette slices in a 375°F (190°C) oven until crisp and lightly golden. For extra flavor, rub with a cut garlic clove.
9. Assemble: Ladle hot soup into broiler-safe bowls.

   Top with a layer of toasted baguette slices. Cover generously with grated Gruyère and a sprinkle of Parmesan if using.
10. Gratinate: Place bowls on a baking sheet and broil until the cheese is melted, bubbling, and browned in spots, 2–4 minutes. Watch closely to avoid burning.
11. Serve: Let sit 2–3 minutes before serving.

    The cheese will be molten. Garnish with a few thyme leaves if you like.

How to Store

• Refrigerator: Store the soup (without bread and cheese) in an airtight container for up to 4 days.
• Freezer: Freeze the soup base for up to 3 months. Thaw in the fridge overnight and reheat gently on the stove.
• Bread and cheese: Keep toasted baguette slices at room temperature for 1–2 days.

  Grate cheese fresh before serving.

• Reheating: Warm the soup on the stove, assemble with toast and cheese, and broil just before serving to refresh the crust.

Health Benefits

• Onion power: Onions are rich in antioxidants like quercetin and contain prebiotic fibers that support gut health.
• Protein and minerals: Good-quality beef stock provides protein and minerals like zinc and iron, especially if it’s bone-based.
• Portion control: The soup is satisfying due to its savory depth, which can help with mindful eating despite the cheese topping.
• Customizable richness: You can reduce butter, choose lighter cheese portions, or use a beef-chicken stock blend to lower the overall heaviness.

Common Mistakes to Avoid

• Rushing the onions: Undercooked onions will taste sharp and flat. Take the full time to caramelize them deeply.
• Too much heat: High heat can scorch onions. Keep it moderate and stir regularly to develop even color.
• Weak stock: A bland broth makes a bland soup.

  Use a robust, low-sodium stock so you control the seasoning.

• Skipping acidity: A touch of vinegar or a splash of sherry at the end keeps the soup from tasting overly sweet or heavy.
• Soggy bread: Always toast the baguette. Crisp bread holds up under the cheese and stays pleasantly chewy.
• Wrong cheese: Avoid pre-shredded blends that don’t melt well. Freshly grated Gruyère gives the best stretch and flavor.

Alternatives

• Vegetarian version: Use a rich vegetable stock or mushroom broth.

  Add a splash of soy sauce or tamari for umami.

• Gluten-free: Skip the flour or use a gluten-free blend. Use gluten-free baguette or toasted rounds.
• No alcohol: Replace wine with extra stock plus 1–2 teaspoons of sherry vinegar for brightness.
• Cheese swaps: Try Comté, Emmental, or a mix of Gruyère and a little sharp cheddar for a punchier flavor.
• Herb accents: Add a bay leaf and thyme as directed, or finish with chives or parsley for a fresh lift.
• Richer finish: Stir in a knob of butter at the end for extra gloss and body.

FAQ

What onions work best for French onion soup?

Yellow onions are the classic choice because they balance sweetness and bite. You can mix in a few red or sweet onions for nuance, but avoid using only sweet onions or the soup may become cloying.

Can I make this without broiler-safe bowls?

Yes.

Toast the bread with cheese on a baking sheet until melted and golden, then float the cheesy toasts on the hot soup in regular bowls.

Do I have to use wine?

No. Replace it with stock and finish with a small splash of vinegar. The acidity is key for balance, so don’t skip that part.

How long should I caramelize the onions?

Plan on 40–55 minutes over medium to medium-low heat.

You want a deep amber color with a jammy texture and no burnt bits.

What’s the best cheese for the gratin topping?

Gruyère is traditional and melts beautifully. Comté or Emmental are excellent alternatives. A small amount of Parmesan adds savory depth.

Why add flour to the onions?

It lightly thickens the broth so it clings to the spoon.

It’s optional; you can skip it for a silkier, more brothy soup.

Can I use store-bought stock?

Absolutely. Choose a low-sodium, high-quality brand. Taste as you go and adjust seasoning carefully.

In Conclusion

Classic French Onion Soup is a masterclass in turning simple ingredients into something memorable.

With patient caramelization, a well-seasoned broth, and a golden lid of melted cheese, it delivers comfort in every spoonful. Make it for a cozy night in, or as a showstopping starter for guests. Either way, it’s the kind of recipe you’ll come back to all winter long.