Photo: Ralph Daily from Birmingham, United States · CC BY 2.0
French Onion Soup
A classic French soup of deeply caramelized onions in rich stock, topped with a baguette and gruyère and broiled until golden. Take your time with the onions and anyone can make it deeply savory.
Ingredients
- Onions · large, thinly sliced, ~800g4
- Butter3 tbsp
- Olive oil1 tbsp
- Sugar · to help caramelize, optional1 tsp
- Flour · to thicken, optional1 tbsp
- White wine · optional, to deglaze100 ml
- Beef stock (or vegetable)1 L
- Thyme · or a little dried2 sprigs
- Salt & pepper1 to taste
- Cheese toast
- Baguette4 slices
- Gruyère (or Emmental) · grated100 g
Steps
- ⏲ 30 min
Melt the butter and olive oil in a wide pot, add the sliced onions, and caramelize over medium-low heat 25–35 minutes, stirring often, until deep golden brown (a little sugar helps). Going slow is the key.
- ⏲ 2 min
Stir in the flour and cook 2 minutes, then pour in the wine and scrape up the bottom as it reduces.
- ⏲ 20 min
Add the stock and thyme, bring to a boil, then simmer 15–20 minutes. Season with salt and pepper.
- ⏲ 5 min
Lightly toast the baguette slices. Preheat the broiler.
- ⏲ 2 min
Ladle the soup into oven-safe bowls, top with the baguette, and cover generously with cheese.
- ⏲ 5 min
Broil 3–5 minutes until the cheese is melted, golden, and bubbling. Serve hot.
Variations
- Vegetarian: Use a rich vegetable stock instead of beef.
- Cheese blend: Mix gruyère with mozzarella and Parmigiano.
- Sherry/cognac: A splash at the end adds depth.
- No bowls: Melt cheese on the toast separately and float it on top.
Tips
- The stock is the whole body of the soup: the strained broth of a pot-au-feu is a traditional base for it. There is nothing else in the bowl to hide behind (stocks and broths).
- Don't rush the onions — slow, deep caramelizing is where the sweetness comes from.
- Deglaze with a little liquid to capture the browned flavor when it sticks.
- Use a rich stock for deep flavor.
- Gruyère melts well and is the classic nutty cheese.
- No oven-safe bowls/broiler? Toast the cheese bread separately and add it on top.
More detail and the reasons why (6)
- Most of the half hour is water leaving, and only the last stretch of it is browning. Four large onions are about 800g, and nearly nine-tenths of that is water. Browning puts dryness first: while water is present the surface stalls at 100°C and essentially nothing happens. So that one line is two phases — a long wet phase where the onions collapse and give up several hundred grams of water, and only then a phase where colour appears. It is also why the recipe asks for a wide pot and no lid. The water has to go somewhere.
- And the time cannot be bought back with heat. The colour is caramelisation, which happens around 160°C (what sugar does); sugar burns easily and is bitter past 190°C with no way back. Raise the flame and the pan reaches that before the middle of the heap has dried. The teaspoon of sugar shortens the colour phase; it does nothing about the water.
- Both browning reactions end up in the same bowl. Caramelisation breaks down sugar alone; the Maillard reaction needs sugar and protein together. The long cook of the onions is caramelisation; the browned cheese on top is Maillard. Japanese curry supplies the other half of the contrast: there the caramelised onion is a sweetness deposited into the liquid, and here it is the dish.
- One tablespoon of flour is not there to make a sauce. It is a white roux, the bottom rung of thickening's ladder — strongest thickening, no flavour of its own — and in a litre of stock it gives the broth just enough body to hold the bread up instead of letting it sink. It needs at least two minutes to cook out the raw flour taste; the wine goes in next and stops the cooking.
- The wine is for deglazing. Deglazing lifts the brown layer off the base of the pot, and the acid and alcohol in wine or beer lift it well. That layer is concentrated caramelisation, so leaving it behind throws away half of what the thirty minutes was for.
- Stale baguette, and Gruyère at the awkward point of the melting scale. Croûtes work better made from stale baguette — made with fresh bread they go to mush. And mid-aged cheese goes oily and clumpy if the heat is too high (dairy and heat), which is the edge a broiler works on: close to the element, watched, three to five minutes, never a long bake.
The basics behind this dish
- Salt: When You Add It Matters More Than How MuchThe same amount of salt either draws water out or seasons all the way through, depending on when it goes in. Osmosis, seasoning in layers, and why salt types are not interchangeable by volume.
- Browning and the Maillard ReactionMeat fails to brown for one of three reasons: it is wet, the pan is cool, or you put too much in at once. Plus how the brown film stuck to the pan becomes your sauce.
- Stocks and Broths: Clarity, Time, and Why You Do Not Salt ThemWhat separates a clear stock from a cloudy one is temperature, not ingredients. Why you start in cold water, how long each ingredient wants, and why salt comes later.
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