French Onion Soup

Alt text: A finished crock of French onion soup gratinée with browned bread, melted cheese, and herbs on top

Cultural Context

French onion soup, or soupe à l'oignon gratinée, is built from humble onions slowly cooked until sweet, then simmered with stock and finished under the broiler with bread and Gruyère. Onion soups have been known in France for centuries, while the cheese-topped gratinée style became associated with Paris market cooking around Les Halles in the 19th century. Today it remains one of the most recognizable French bistro dishes: simple, warming, and deeply savory when the onions are cooked patiently.

Ingredients

Main Components

• 90 g (6 tbsp) unsalted butter
• 1.4 kg (3 lb / about 6 large) yellow onions or mixed yellow, sweet, red onions, and shallots, sliced 3 mm (1/8 inch) thick
• 8 g (1 1/2 tsp) kosher salt, plus more to taste
• Freshly ground black pepper, to taste
• 120 ml (1/2 cup) dry sherry, dry white wine, or dry vermouth
• 1.8 L (2 qt / 8 cups) homemade beef stock or good low-sodium chicken stock
• 2 sprigs fresh thyme
• 1 bay leaf
• 5 ml (1 tsp) cider vinegar

For the Gratinée

• 8 bowl-size slices rustic French bread or baguette, toasted until crisp
• 15 g (1 tbsp) unsalted butter, softened, for the toast
• 1 medium garlic clove, peeled and halved
• 450 g (1 lb / about 4 packed cups) Gruyère cheese, coarsely grated
• 2 tbsp minced fresh chives or parsley, for serving

Substitutions:

• Gruyère → Comté or Emmental for a traditional Alpine-style melt
• Dry sherry → Dry white wine, dry vermouth, or Madeira; avoid sweet cooking wine
• Beef stock → Rich chicken stock works well if it tastes clean and savory
• Rustic French bread → Baguette slices or another sturdy crusty bread that can hold up in soup

Equipment

• Large stainless steel, cast-iron, or heavy-bottomed pot
• Wooden spoon or heatproof spatula
• Ladle
• 4 oven-safe soup crocks or bowls
• Rimmed baking sheet
• Broiler

Instructions

Preparation (Active time: 15 min)

1. Slice the onions: Trim, halve, peel, and slice the onions into even 3 mm (1/8 inch) half-moons. Keep the slices fairly uniform so they soften and brown at the same pace.

2. Prepare the gratin toppings: Toast the bread until dry and crisp all the way through. Butter one side lightly, then rub the warm toast with the cut garlic clove until fragrant. Grate the cheese and keep it chilled until needed.

Cooking (Active time: 20 min)

3. Start the onions: Melt 90 g butter in a large heavy pot over medium-high heat until foaming. Add the onions and salt, stir well, and cook until the onions collapse and release their moisture, about 8-10 minutes.

4. Caramelize slowly: Reduce heat to medium-low. Cook, stirring often, until the onions are very soft, sweet, and an even deep golden brown, 60-90 minutes. If browned sugars on the bottom threaten to scorch, add 15 ml (1 tbsp) water and scrape them back into the onions. Avoid rushing this step; burned onions will make the soup bitter.

5. Deglaze: Add the sherry and scrape the bottom of the pot thoroughly. Simmer until the sharp alcohol aroma fades and the liquid is mostly absorbed, about 3 minutes.

6. Simmer the soup: Add the stock, thyme, and bay leaf. Bring to a simmer, reduce heat to maintain gentle bubbling, and cook uncovered for 20 minutes. Stir in the cider vinegar, then season with salt and pepper. Discard the thyme stems and bay leaf.

Assembly & Finishing

7. Fill the crocks: Heat the broiler and set a rack near the top of the oven. Place 4 oven-safe bowls on a rimmed baking sheet. Ladle a little soup into each bowl, add one toast and a small handful of cheese, then fill nearly to the top with more soup and onions.

8. Gratinate: Set a second toast on each bowl, pressing it just into the soup. Cover generously with the remaining Gruyère. Broil until the cheese is melted, bubbling, and browned in spots, 2-5 minutes depending on your broiler.

9. Garnish and serve: Let the bowls stand for 2 minutes so the cheese settles slightly. Garnish with chives or parsley and serve hot, warning diners that the crocks are very hot.

Food Safety & Storage

• Minimum safe internal temperature: No meat requires endpoint cooking in this recipe; reheat leftover soup to 165°F (74°C) before serving.
• Storage: Refrigerate soup without bread and cheese in an airtight container for up to 4 days.
• Freezing: Freeze the soup base without bread or cheese for up to 3 months. Thaw overnight in the refrigerator before reheating.
• Reheating: Warm the soup base gently on the stovetop, then assemble with fresh toast and cheese and broil just before serving.

Serving Suggestions

• Serve as a first course or as a light meal with a crisp green salad.
• Pairs well with Beaujolais, dry cider, or the same dry sherry or white wine used in the pot.
• Traditional serving style: individual oven-safe crocks with bubbling cheese over toasted bread.

Scaling Notes

Half recipe (1/2x): Use a wide skillet or small heavy pot so the onions still have room to brown; caramelization time may be closer to 45-60 minutes.

Double recipe (2x): Use two wide pans for caramelizing the onions, then combine them in a stockpot before adding liquid. Broil bowls in batches so each gratin browns evenly.

Chef's Notes

• Sourcing: Choose onions that are firm and heavy for their size. Homemade beef stock is ideal, but a clean, gelatin-rich chicken stock often tastes better than a dull boxed beef broth.
• Make-ahead: The soup base is excellent made 1-2 days ahead. Reheat and gratinate with fresh toast and cheese just before serving.
• Variations: Some Parisian-style versions use a little flour for body; stir 1 tbsp flour into the caramelized onions for 2 minutes before deglazing if you prefer a slightly thicker soup.
• Common pitfalls: Do not cook the onions over high heat until dark or blackened; the target is soft, sweet, and deep golden brown. Toast the bread thoroughly so it absorbs broth without dissolving immediately.

Nutrition Information (Optional)

Per serving: approximately 900 kcal

• Protein: 42g | Fat: 52g | Carbohydrates: 64g | Fiber: 6g

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Sources

• Serious Eats, "French Onion Soup (Soupe à l'Oignon Gratinée)": https://www.seriouseats.com/french-onion-soup-recipe
• Epicurious / Gourmet, "Soupe a l'Oignon au Fromage (French Onion Soup)": https://www.epicurious.com/recipes/food/views/soupe-a-loignon-au-fromage-french-onion-soup-11047
• Wikipedia, "French onion soup" historical overview and ingredient notes: https://en.wikipedia.org/wiki/French_onion_soup
• Image source: Wikimedia Commons, "French Onion Soup (6635668505).jpg" by Ralph Daily, licensed CC BY 2.0: https://commons.wikimedia.org/wiki/File:French_Onion_Soup_(6635668505).jpg

Version History:

• v1 (2026-07-16): Initial recipe by @Codex

Credits:

• Recipe development: @Codex, synthesized from the sources above
• Testing: @Codex
• Verification: @Coordinator
• Photography: Ralph Daily via Wikimedia Commons, CC BY 2.0; source URL listed above

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Recipe Location: /Recipes/french/french_french-onion-soup_v1.md
Images Location: /Images/french-onion-soup/