Soupe à l’Oignon (French Onion Soup)
Why this recipe works
- Deep onion flavour: Slow caramelisation turns the onions sweet, jammy and savoury, giving the soup its distinctive depth.
- Classic gratinée finish: Toasted baguette and Gruyère are grilled over the hot soup to create the bubbling, golden crust that defines the dish.
- Easy to prepare ahead: The soup base stores well without the bread and cheese, so only the final topping needs to be finished before serving.
Get the most out of this recipe
Timing notes
- Most of the time is caramelising: The active work is modest, but the onions need patient cooking to develop sweetness and colour without burning.
- Serve after grilling: Once the baguette and Gruyère are grilled, serve the soup straight away while the topping is crisp at the edges and molten underneath.
Ingredient notes
- Slice onions evenly: Even slices cook at the same rate, helping the onions soften and caramelise without some pieces scorching before others are ready.
- Use a good melting cheese: Gruyère gives the topping its nutty flavour and smooth melt; Emmental is a milder alternative with a more elastic texture.
- Wine adds balance: Dry white wine lifts the richness of the stock and onions; extra stock can be used instead for an alcohol-free version.
Common mistakes
- Do not rush the onions: High heat can make the onions bitter before they become sweet. Lower the heat once they start colouring and stir regularly.
- Avoid soft bread: Toast the baguette before adding it to the bowls so it can hold up under the cheese and hot soup.
Make-ahead tips
- Make the soup base in advance: Cook and chill the soup without the baguette and cheese, then reheat gently before adding the topping.
- Freeze without the topping: The onion soup base can be frozen, but the bread and Gruyère should be added fresh after reheating.
- Reheat before grilling: Bring the soup back to piping hot in a saucepan before ladling it into bowls, so the topping grills quickly without cooling the soup.
Equipment you'll need
Ingredients
Instructions
- Halve and thinly slice the onions. Set a large pot over medium heat and melt the butter, then add the onions, salt and pepper. Cook for 10 minutes, stirring often, until the onions soften and begin to turn golden.
- Reduce the heat to medium-low and cook the onions, stirring and scraping the base of the pot regularly, until deeply caramelised and jammy. If they start to catch, add a small splash of water and keep stirring. This slow stage is key for sweetness and depth.
- Add the thyme and bay leaves, then pour in the wine and bring to a lively simmer. Cook for 3 to 5 minutes, scraping up any browned bits, until the wine has reduced slightly and the alcohol smell has cooked off.
- Add the beef stock and bring to a gentle simmer. Cook for 20 minutes so the flavours meld, then taste and adjust with a little more salt and pepper if needed. Keep the soup hot while you prepare the topping.
- Heat the grill to high and toast the baguette slices on a baking tray until lightly golden on both sides. Ladle the hot soup into oven-safe bowls, float 2 baguette slices on each, and pile the Gruyère on top. Grill for 2 to 4 minutes until bubbling and deeply golden in spots, then serve straight away.
Recipe notes
Tips
- Slice the onions evenly so they caramelise at the same rate, and keep the heat low once they start colouring to avoid bitterness.
- For the best crust, grate the Gruyère finely so it melts quickly and browns before the bread softens too much.
- If serving children, grill the bowls on a baking tray and let them stand for 2 minutes before serving, as the cheese topping stays very hot.
Substitutions
- Replace Dry White Wine with the same amount of Beef stock for an alcohol-free version.
- Replace Gruyère cheese with Emmental cheese for a milder, more elastic melt.
- Replace Unsalted butter with Olive oil for a lighter finish, keeping the heat low to prevent scorching.
Storage
- Refrigerate up to 3 days
- Store the soup (without baguette and Gruyère) in an airtight container. Reheat gently in a saucepan until piping hot, then add fresh toasted baguette and cheese and grill to serve. Freeze the soup base for up to 3 months; defrost overnight in the fridge before reheating.
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Recipe overview
- Servings: 4 servings
- Total time: 1h 35min (25min active)
- Difficulty: Medium
- Cuisine: French
-
Allergens:
Gluten Milk Wheat
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