Soupe à l’Oignon Gratinée (French Onion Soup with Gruyère Toast)
Why this recipe works
- Deep onion flavour: Slow caramelising turns the onions sweet, jammy and deeply savoury before the stock is added.
- Classic gratinée finish: Toasted baguette and Gruyère create the bubbling, golden topping that makes this soup distinctive.
- Balanced richness: Dry white wine lifts the beefy broth and cuts through the butter, onions and melted cheese.
Get the most out of this recipe
Timing notes
- Most of the time is hands-off: The active work is mainly slicing, stirring and assembling; the flavour develops during the slow onion caramelisation and simmering.
- Serve straight after grilling: Once the cheese is bubbling and golden, serve immediately so the toast stays crisp at the edges and the topping remains molten.
Ingredient notes
- Use yellow onions: Yellow onions caramelise well and give the soup a rounded sweetness without becoming overly sharp.
- Gruyère matters: Gruyère gives the best balance of nutty flavour and smooth melt; Emmental is a milder alternative.
- Wine adds lift: Dry white wine brings acidity and depth, but extra beef stock can be used instead for an alcohol-free version.
Common mistakes
- Do not rush the onions: High heat can scorch the onions before they caramelise. Keep the heat moderate and add a splash of water if the base starts to catch.
- Avoid soft, soggy toast: Toast the baguette before adding it to the soup so it holds its structure under the cheese.
- Watch the grill closely: The cheese can move from golden to burnt quickly, so keep an eye on it during the final few minutes.
Make-ahead tips
- Make the soup base ahead: The onion broth can be cooked in advance, cooled quickly and refrigerated without the bread or cheese.
- Freeze without toppings: Freeze only the soup base, then defrost and reheat before adding freshly toasted baguette and Gruyère.
- Reheat gently: Warm the soup in a saucepan until piping hot, then assemble and grill the bowls just before serving.
Equipment you'll need
Ingredients
Soup
Gratin topping
Instructions
- Melt the butter with the olive oil in a large pot over medium heat. Add the onions with the salt and cook for 10 minutes, stirring often, until softened and starting to turn golden.
- Reduce the heat to medium-low and continue cooking the onions, stirring regularly and scraping the base, until deeply caramelised and jammy. This should take 35 to 45 minutes; if they start to catch, add a splash of water and keep going.
- Stir in the garlic and black pepper and cook for 1 minute until fragrant. Pour in the wine and simmer for 3 to 5 minutes, scraping up any browned bits, until reduced by about half.
- Add the beef stock, thyme and bay leaves. Bring to a gentle simmer, then cook for 20 minutes so the flavours meld; taste and adjust with a little more salt if needed.
- Meanwhile, heat the grill to high and set the baguette slices on a baking tray. Toast for 1 to 2 minutes per side until crisp and lightly golden, watching closely.
- Grate the Gruyère. Remove and discard the thyme sprigs and bay leaves from the soup, then ladle into heatproof bowls set on a baking tray; float 2 baguette slices on each and pile the cheese on top.
- Grill for 2 to 4 minutes until the cheese is bubbling and golden in spots. Serve immediately while piping hot.
Recipe notes
Tips
- Caramelise the onions slowly over medium-low heat for the deepest flavour; they should be mahogany-brown, not burnt.
- Use heatproof bowls and place them on a baking tray before grilling to make them easier and safer to handle.
- If serving children or anyone sensitive to alcohol, simmer the wine until the sharp aroma has cooked off before adding the stock.
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 slightly milder, more elastic melt.
- Replace Fresh thyme with 1 tsp Dried thyme for a pantry-friendly option.
Storage
- Refrigerate up to 3 days
- Cool the soup (without baguette and cheese) quickly, then refrigerate in a sealed container. Reheat gently in a saucepan until piping hot, then add fresh toasted baguette and Gruyère 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 30min (30min active)
- Difficulty: Medium
- Cuisine: French
-
Allergens:
Gluten Milk Wheat
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