French Onion Soup with Gruyère Toasts
Why this recipe works
- Deep savoury base: Slowly caramelised onions give the soup its sweetness, colour and rounded savoury depth before the stock is added.
- Classic gratin finish: Baguette and Gruyère are baked directly over the soup, creating the familiar melted, bubbling topping.
- Rich broth, crisp toast: The toasted bread softens where it meets the soup while keeping some structure beneath the melted cheese.
- Easy to prepare in stages: The soup base can be made ahead, then reheated and finished with fresh toasts and cheese just before serving.
Get the most out of this recipe
Timing notes
- Most of the time is in the onions: The active preparation is modest, but the caramelising stage needs steady, patient cooking for the best flavour.
- Serve after baking: Once the Gruyère is melted and bubbling, serve straight away so the toast keeps its best texture.
Ingredient notes
- Use yellow onions: Yellow onions are a good choice because they caramelise well and bring balanced sweetness without becoming too sharp.
- Gruyère matters: Gruyère gives the topping its nutty flavour and smooth melt; Emmental is a milder alternative if preferred.
- Wine balances the broth: White wine adds brightness to the rich stock and onions; dry sherry gives a deeper, slightly sweeter result.
Make-ahead tips
- Make the soup base ahead: Cook and cool the soup without the bread or cheese, then refrigerate until needed.
- Freeze without the topping: Freeze only the soup base, then add freshly toasted baguette and Gruyère after reheating.
- Reheat gently: Warm the soup in a saucepan until piping hot before transferring to ovenproof bowls for the cheese-topped finish.
Common mistakes
- Do not rush the onions: High heat can burn the onions before they caramelise properly; keep the heat controlled and scrape the base often.
- Avoid reducing too far: Simmer the broth gently so the soup stays spoonable rather than becoming overly concentrated.
- Toast before topping: Baguette slices should be golden before they go onto the soup, otherwise they can collapse too quickly under the cheese.
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, stirring often, for 10 minutes until the onions soften and start to turn pale gold.
- Reduce the heat to medium-low and continue cooking, stirring and scraping the base of the pot, until the onions are deeply caramelised and jammy. If they start to catch, add a splash of the wine and scrape up the browned bits. This slow stage is where the flavour develops, so take your time.
- Add the thyme and bay leaves, then pour in the remaining wine and simmer for 2 minutes to cook off the alcohol. Add the beef stock, bring to a gentle simmer, then cook for 20 minutes so the flavours meld. Taste and adjust with a little more salt and pepper if needed.
- Heat the grill to high and set the oven to 200°C (390°F). Arrange the baguette slices on a baking tray and toast under the grill for 1 to 2 minutes per side until golden. Keep an eye on them as they colour quickly.
- Ladle the hot soup into ovenproof bowls and discard the thyme sprigs and bay leaves. Float 2 to 3 baguette toasts on each bowl, then top generously with the Gruyère. Bake until the cheese is melted and bubbling, 6 to 8 minutes, then serve straight away.
Recipe notes
Tips
- For the best flavour, keep the heat low during caramelising and stir regularly, scraping the base so the onions brown evenly rather than burn.
- If serving to children or anyone avoiding alcohol, simmer the wine for the full 2 minutes before adding the stock so the harsh alcohol notes cook off.
Substitutions
- Replace Gruyère cheese with Emmental cheese for a milder, slightly nuttier topping.
- Replace white wine with dry sherry for a deeper, more rounded sweetness.
Storage
- Refrigerate up to 3 days
- Cool the soup quickly, then refrigerate in a sealed container for up to 3 days. Freeze the soup (without baguette and cheese) for up to 3 months; defrost overnight in the fridge and reheat gently in a saucepan until piping hot, then add freshly toasted baguette and Gruyère to serve.
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Recipe overview
- Servings: 4 servings
- Total time: 1h 25min (25min active)
- Difficulty: Medium
- Cuisine: French
-
Allergens:
Gluten Milk Wheat
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