French Onion Soup with Gruyère Crouton
Why this recipe works
- Slow caramelisation: Cooking the onions gradually builds the soup’s signature sweetness, colour and savoury depth.
- Layered savoury base: White wine lifts the browned onion base, while beef stock, thyme and bay add depth without overwhelming the onions.
- Bright finish: A little sherry vinegar at the end sharpens the broth and balances the richness of the cheese-topped crouton.
Get the most out of this recipe
Timing notes
- Most of the time is onion cooking: The active work is modest, but the onions need 35 to 45 minutes to caramelise properly; rushing this step gives a flatter soup.
- Grill just before serving: Add the toasted baguette and Gruyère only when the soup is hot and ready to serve, so the crouton stays crisp at the edges.
Common mistakes
- Avoid scorching the onions: Lower the heat if the onions catch on the base of the pan; deep browning is desirable, but burnt edges can make the broth bitter.
- Do not skip reducing the wine: Letting the wine reduce before adding stock softens its sharpness and concentrates the flavour in the soup base.
Make-ahead tips
- Make the soup base ahead: The onion broth can be cooked in advance and refrigerated, then reheated gently before adding the croutons and cheese.
- Freeze without the topping: Freeze only the soup base; add freshly toasted baguette and Gruyère after reheating for the best texture.
Ingredient notes
- Use yellow onions: Yellow onions give a good balance of sweetness and savoury depth once caramelised.
- Gruyère matters: Gruyère melts smoothly and browns well under the grill, giving the soup its classic nutty, savoury finish.
- Keep the bread sturdy: A slightly stale baguette holds its shape better on the soup and is less likely to turn soft immediately.
Equipment you'll need
Ingredients
Instructions
- Peel the onions, halve them through the root, then slice thinly. Set a large casserole over medium heat and melt the butter.
- Add the onions and cook, stirring often, for 35 to 45 minutes until deeply caramelised and jammy; lower the heat if they start to catch. Aim for a deep golden brown colour for the best flavour.
- Add the thyme and bay leaves, then pour in the wine and scrape up any browned bits from the base. Simmer for 3 to 5 minutes until the wine has reduced by about half.
- Add the beef stock and bring to a gentle simmer. Cook for 20 minutes so the flavours meld, then stir in the sherry vinegar and remove the thyme sprigs and bay leaves.
- 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.
- Ladle the hot soup into oven-safe bowls and float 2 baguette slices on each. Top generously with the Gruyère and grill for 2 to 4 minutes until melted, bubbling, and browned in spots.
Recipe notes
Tips
- For the deepest flavour, keep the onions moving as they caramelise and adjust the heat so they brown slowly rather than scorch.
- If serving to children, grill the cheese-topped croutons on the tray first, then place them on the soup at the table to reduce the risk of splashes.
Substitutions
- Replace Dry White Wine with the same amount of Beef stock, adding the Sherry vinegar at the end as written for brightness.
- Replace Gruyère cheese with Emmental cheese for a similar melt and a slightly milder flavour.
Storage
- Refrigerate up to 3 days
- Cool the soup quickly, then refrigerate in a sealed container. Freeze the soup without the baguette and cheese; defrost overnight in the fridge and reheat gently in a saucepan until piping hot, then add freshly toasted baguette and Gruyère and grill to serve.
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Recipe overview
- Servings: 4 servings
- Total time: 1h 25min (30min active)
- Difficulty: Medium
- Cuisine: French
-
Allergens:
Gluten Milk Wheat
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