Summary: This classic French Onion Soup Gratinée relies on the slow caramelisation of yellow onions to develop a deep, sweet, and savoury base. Finished with a toasted baguette slice and a golden, bubbly layer of melted Gruyère cheese, it is the quintessential bistro comfort food. Preparation takes approximately 2 hours, including the patient caramelisation process, and serves 6 people as a hearty starter.
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Category: Soups, French Cuisine
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Quick overview
- Dish: French Onion Soup Gratinée
- Category: Soups, French Cuisine
- Cuisine: French
- Main ingredient: Yellow onions, 1.5 kg (high quality, firm)
- Guide: 12 most popular French dishes: favourite recipes of French cuisine
- Total time: 130 minutes (20 min prep + 110 min cooking)
- Difficulty: Medium
- Portions: 6 (Portion weight: 450 g)
- Key technique: Caramelisation
- Preparation types: Sautéing, simmering, grilling
- Dietary info & Allergens: Contains: Gluten, Milk, Celery
- Suitable for: Vegetarians (if using vegetable stock)
- Nutritional values (per 1 portion): 320.5 kcal, Protein: 12.4 g, Fat: 14.2 g, Carbohydrates: 36.8 g
- Storage: 3 days in the fridge, 3 months in the freezer
- Pairing: Lager, Chardonnay, Sparkling water
- In short: A deeply flavoured, rich onion soup topped with toasted bread and bubbly, melted cheese.
- Last updated: 21 September 2026
WAGUU says: “The secret to a perfect onion soup lies in the patience of caramelising the onions until they reach a deep mahogany colour, ensuring the base is naturally sweet and complex.”
How to take it further: Add a splash of dry sherry at the end for extra depth, or infuse the soup with a fresh sprig of thyme during the simmering phase.
Key facts
| Prep time: | 20 minutes |
| Cooking time: | 110 minutes |
| Temperature: | 180 °C (grill) |
| Number of portions: | 6 |
In a nutshell
French Onion Soup Gratinée is a timeless culinary masterpiece that transforms humble yellow onions into a rich, velvety broth. When combined with crusty bread and a generous layer of melted, nutty Gruyère, it becomes a comforting bowl of pure joy.
Ingredients
Base portions: 6 portions • Portion weight: 450 g
| Ingredient | Amount | Quality |
|---|---|---|
| Yellow onions | 1.5 kg | Firm, dry |
| Unsalted butter | 60 g | High-fat |
| Beef stock | 1.5 l | Strong, homemade |
| Plain flour | 30 g | Fine |
| Baguette | 1 piece | Freshly baked |
| Gruyère cheese | 200 g | Aged |
| Salt | 18 g | Fine sea salt |
Why you will love this recipe
- Depth of flavour: The slow caramelisation of onions builds a complex, natural sweetness that defines the dish.
- Texture contrast: The combination of soft, melting onions, soaked bread, and crispy, browned cheese provides a satisfying mouthfeel.
- Comfort factor: A steaming bowl of this soup is the ultimate remedy for cold days and long evenings.
Success guaranteed: By following the specific caramelisation time and using a high-quality, strong beef stock, you will achieve professional results every time.
Recipe overview
Prep: 20 min | Cooking: 110 min | Difficulty: Medium | Portions: 6 | Type: Soup | Origin: French
Detailed instructions
Overall progress: 0% complete
Phase 1: Onion Preparation – 10 min
Appliances: Hob
1. Peel the onions and slice them into thin, uniform half-moons. Visual check point (VKB): The onions should be consistently sliced to ensure even cooking.
VKB: Uniform onion slices.
Phase 2: Caramelisation – 60 min
Appliances: Hob
2. Melt the butter in a large, heavy-bottomed pot over medium heat. Add the onions and a pinch of salt. Cook, stirring occasionally, for 60 minutes until they reach a deep, rich mahogany colour. VKB: The onions must be soft, dark, and sweet, not burnt.
VKB: Mahogany colour reached.
Before moving to the next step:
Ensure the onions are fully caramelised; otherwise, the soup will lack the necessary depth.
Phase 3: Building the Soup – 30 min
Appliances: Hob
3. Sprinkle the flour over the caramelised onions and stir for 2 minutes to cook out the raw taste. Gradually pour in the beef stock, stirring constantly to prevent lumps. Simmer for 28 minutes. VKB: The soup should have a slightly thickened, velvety consistency.
VKB: Correct consistency.
Phase 4: Bread Preparation – 5 min
Appliances: Grill
4. Slice the baguette into 2 cm thick rounds. Toast them under the grill until golden brown on both sides. VKB: The bread must be crisp to hold its structure in the soup.
VKB: Golden and crisp.
Phase 5: Gratinée – 5 min
Appliances: Grill
5. Ladle the hot soup into heat-proof bowls. Place a toasted baguette slice on top and cover with a generous layer of grated Gruyère cheese. Grill until the cheese is bubbling and golden. VKB: The cheese must be perfectly melted and slightly browned.
VKB: Bubbly, golden cheese.
Required equipment
| Utensil | Ideal size | Alternative | Risk |
|---|---|---|---|
| Heavy-bottomed pot | 4 l | Dutch oven | Burning onions |
| Heat-proof bowls | 500 ml | Ramekins | Breaking |
| Grill | High setting | Oven broil | Overcooking cheese |
Shopping list
Nutritional profile
Values per 1 portion (excluding side dishes). Calculated from average nutritional values of ingredients.
| Nutrient | Per 100 g | Per 1 portion | Per 6 portions |
|---|---|---|---|
| Energy | 71.2 kcal | 320.5 kcal | 1923.0 kcal |
| Fat | 3.1 g | 14.2 g | 85.2 g |
| of which saturates | 1.8 g | 8.1 g | 48.6 g |
| Carbohydrates | 8.2 g | 36.8 g | 220.8 g |
| of which sugars | 3.5 g | 15.8 g | 94.8 g |
| Protein | 2.8 g | 12.4 g | 74.4 g |
| Salt | 0.9 g | 4.0 g | 24.0 g |
Reference intake of an average adult (8400 kJ / 2000 kcal).
WAGUU Pro Level
- Pro standard: Verified recipe with precise ratios and visual control points.
- Tip 1: Use a mix of yellow and red onions for a more complex flavour profile.
- Tip 2: Deglaze the pot with a splash of white wine before adding stock to capture all the flavourful brown bits (fond).
- Tip 3: Ensure the bread is toasted thoroughly to prevent it from turning into a mushy paste in the soup.
- Tip 4: Rub the toasted bread with a clove of garlic for an extra aromatic kick before placing it in the soup.
Scientific background
The flavour of French Onion Soup is primarily driven by the Maillard reaction, a chemical reaction between amino acids and reducing sugars that gives browned food its distinctive flavour. During the long caramelisation process, the onions’ natural sugars break down, and the cell structure collapses, resulting in a rich, sweet, and complex base. The addition of flour creates a roux, which provides the soup with its characteristic body and velvety mouthfeel.
Fine Dining – Professional techniques
- Plate composition: Serve in individual ceramic bowls to maintain the heat and provide a perfect vessel for the gratinée layer.
- Textural contrasts: The contrast between the crunchy top of the baguette and the soft, soaked base is essential.
- Temperature contrast: The soup must be piping hot, while the cheese should be just beginning to cool and set.
- Aromatic garnishes: A light dusting of fresh thyme leaves adds a bright, herbal note that cuts through the richness of the cheese.
Sensory radar
- Appearance: A deep, dark brown broth topped with a golden, bubbly cheese crust.
- Aroma: Intense, sweet caramelised onion notes with a hint of toasted cheese and beef.
- Taste: Deeply savoury, slightly sweet, and rich with a nutty finish from the Gruyère.
- Texture: Velvety, smooth broth with soft onions and a crisp, chewy bread component.
Pairing
- BEER: A crisp, dry lager balances the richness of the soup perfectly.
- WINE: A buttery Chardonnay complements the nutty profile of the Gruyère cheese.
- NON-ALCOHOLIC: Sparkling water with a twist of lemon cleanses the palate between rich bites.
Various preparation variants
- Vegetarian Version: Replace the beef stock with a rich, roasted vegetable stock and ensure the cheese is vegetarian-friendly.
- Herb-Infused Version: Add fresh thyme, bay leaves, and parsley during the simmering stage for a more aromatic and herbal depth.
Allergens and dietary information
Contains: Gluten, Milk, Celery • Gluten: The baguette and flour contain gluten. • Not suitable for: Vegans (contains dairy and beef stock).
Suitable for
This soup is ideal for a comforting weekend meal, a starter for a festive dinner, or a hearty lunch on a cold winter day.
Substitution catalog
- Gruyère cheese: Emmental or Comté can be used as a substitute with similar nutty characteristics.
- Baguette: Any crusty, dense bread will work if a baguette is not available.
FAQ
Can I use pre-caramelised onions?
No, the process of slow caramelisation is essential for developing the deep, rich flavour profile of this soup.
How do I prevent the bread from turning to mush?
Toast the bread well until it is very crisp, and place it on top of the soup just before grilling.
Can I make this soup in advance?
Yes, the soup base actually tastes better the next day as the flavours have more time to meld.
What if I don’t have heat-proof bowls?
You can grill the cheesy bread separately and place it on top of the hot soup just before serving.
WAGUU Petr advises: Cooking for 12 or more people?
12–16 people: Double the recipe and use two large pots for caramelising the onions to ensure even heat distribution. 20+ people: Prepare the soup base a day in advance; the flavour will improve, and it will be easier to manage the final assembly on the day of the event.
Sides and Serving
- Green salad – A light vinaigrette salad cuts through the richness (not included in the recipe)
- Red wine – A full-bodied red pairs well with the beef stock (not included in the recipe)
Serving: Serve immediately in the bowls you used for grilling, taking care as they will be very hot.
Storage and reheating
Fridge: 3 days • Freezer: 3 months • Reheating: Reheat the soup base on the hob and toast fresh bread and cheese separately.
Author: WAGUU Petr & Team • Published: 21 Sep 2026 • Updated: 30 Oct 2026
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Common mistakes
- Under-caramelising: The onions will be pale and lack the necessary sweet, deep flavour.
- Burning the onions: High heat will make the onions bitter; always use medium to low heat.
- Soggy bread: Adding bread too early or not toasting it enough will lead to a disintegrated, mushy texture.
- Using weak stock: The stock is the foundation; a weak stock will result in a bland, watery soup.