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Classic French Onion Soup: The Definitive Recipe
Recipe··8 min read

Classic French Onion Soup: The Definitive Recipe

French onion soup is the definitive example of what happens when you apply time and technique to the humblest of ingredients. Onions are cheap. Good beef stock is not, but it is achievable. A handful of other things — bread, Gruyère, wine, thyme — and you have one of the most deeply satisfying soups in existence. The technique is straightforward. What it requires is patience, specifically the patience to caramelise onions properly.

The onions: the only thing that matters

French onion soup has one crucial step and that is caramelising the onions. Properly caramelised onions take 45 minutes to an hour over medium-low heat. Every recipe that claims you can do it in 15 or 20 minutes is lying, or producing something categorically different from what the recipe intends. Properly caramelised onions are deep mahogany brown, sweet, silky, concentrated, and smell like a combination of caramel and beef. Quickly softened onions are pale, watery, and have none of that depth.

Use yellow or brown onions — they have the right balance of sugar and sharpness for this dish. White onions are too mild. Red onions will work but produce a muddy colour. You will need approximately 1.5kg of onions for four servings, because they reduce dramatically during caramelisation.

Slice the onions thinly — about 3 to 4mm. Melt 40g of unsalted butter and a glug of olive oil together in a large heavy pot over medium heat. Add all the onions with a generous pinch of salt. The salt draws out moisture and speeds the process slightly. Stir to coat.

Now reduce the heat to medium-low and cook, stirring every 5 to 10 minutes. For the first 20 minutes, the onions will steam and soften in their own liquid. Then the liquid evaporates, the onions begin to colour, and this is when you must pay attention. If the bottom of the pot is darkening too fast, deglaze with a splash of water or wine and scrape up the browned bits — those are flavour, not burnt residue. Continue cooking and stirring until the onions are a deep, uniform brown and smell unmistakably of caramel. This takes 45 minutes at minimum.

The stock

A good beef stock is the backbone of this soup. Homemade is significantly better than shop-bought, but a good-quality shop-bought stock will still produce an excellent result. What will not work is water with a stock cube — the soup will taste thin and artificial rather than deeply savoury.

If you are making your own stock, see our separate guide on beef stock. For this recipe, you will need one litre of strong, dark, well-seasoned beef stock.

The full recipe

Ingredients for 4 servings:

Method

Caramelise the onions as described above. When they are deeply browned, add the garlic and cook for 2 minutes. Add the wine or sherry and scrape up any remaining browned bits from the bottom of the pot. Let it reduce almost completely — about 3 minutes. Add the stock, thyme, and bay leaf. Season with salt and pepper. Bring to a simmer and cook for 20 minutes to let the flavours meld. Taste and adjust seasoning — the soup should taste intensely savoury with a background sweetness from the onions.

To serve: preheat your grill to high. Ladle the soup into oven-safe bowls — individual crocks with handles are traditional, but any oven-safe bowl works. Place one or two slices of toasted bread on top of each bowl. Cover generously with grated Gruyère, ensuring it reaches the edges of the bowl — this prevents the soup from bubbling up around the cheese.

Place the bowls on a baking sheet and slide under the grill. Watch carefully — you want the cheese to bubble and spot brown in places, which takes 3 to 5 minutes depending on your grill. Serve immediately, with caution — the bowls will be extremely hot.

Variations worth knowing

Wine: The traditional version uses white wine, but dry sherry adds a nutty depth that works beautifully. Red wine is sometimes used and produces a darker, richer soup. Cognac or brandy, added after the onions and flambéed, is the more extravagant restaurant approach.

Cheese: Gruyère is standard. Comté is excellent and slightly more complex. Emmental works but is blander. Avoid pre-grated bags of "Swiss cheese" — they contain cellulose that prevents proper melting and browning.

Bread: The toast must be dry and sturdy enough not to immediately dissolve into the soup. Day-old bread, sliced thick and toasted until crisp all the way through, is ideal. Fresh bread will go soggy before the cheese is done.

Making it ahead

The soup base — without the bread and cheese — keeps in the fridge for 4 days and actually improves. Caramelise the onions and make the broth in advance, refrigerate, and add the toast and cheese topping when ready to serve. This makes French onion soup practical for a dinner party — the long active time moves to whenever suits you, and the final assembly and grilling takes five minutes.