French Onion Soup

French Onion Soup (Soupe à l’oignon gratinée)

In French: soupe à l’oignon gratinée, meaning “onion soup au gratin.” In Hebrew it is called “מרק בצל צרפתי” (French onion soup) and sometimes simply “מרק בצל” (onion soup). The full name matters, because it contains the difference: the soup itself is onion and broth, and the gratinée — a slice of bread and cheese melted on top — is a separate layer that adds more calories than the whole soup.

This is a poverty-kitchen recipe that became a restaurant dish: four cheap ingredients, and above all time. Everything here is onion caramelized very slowly, and any attempt to shorten that step produces a completely different soup.

Prep time: 20 minutes · Cook time: 75 minutes · Total: about an hour and a half · Yield: 6 servings · Difficulty: medium

45 minutes of caramelizing — and why you can’t shorten them

Onions contain sugars (mainly fructose) and amino acids, and under prolonged heat they undergo two processes in parallel: caramelization of the sugars and the Maillard reaction between sugars and proteins. Both need time and moderate temperature. Over high heat the onion simply burns at the edges before its center has had a chance to change — the result is bitter, not sweet.

The surprising practical rule is not to stir too much: the onion needs to sit in contact with the bottom of the pot for 5-7 minutes between stirs, so a brown layer can form. That layer stuck to the bottom (fond) is the flavor — and every time you add a spoonful of water or wine and scrape it up, it dissolves into the soup.

After 45 minutes, 1.5 kg of onions end up at about a third of their starting volume. That’s normal: the water has evaporated and the sugars have concentrated.

Ingredients (for 6 servings)

For the soup:

• 1.5 kg onions — about 6 large onions — thinly and evenly sliced
• 3 tablespoons butter (about 42 grams)
• 1 tablespoon olive oil
• 1 teaspoon sugar (speeds caramelizing, optional)
• 1/2 teaspoon salt, for the start of caramelizing
• 2 cloves garlic, sliced
• 2 tablespoons flour
• 150 ml dry white wine (or red wine; can be replaced with broth)
• 1.5 liters good-quality beef broth — chicken broth works, vegetable broth will give a weaker soup
• 2 bay leaves, 4 sprigs thyme
• 1 tablespoon wine vinegar or brandy, at the end
• Black pepper, and salt to taste

For the topping (for 6 bowls):

• 12 thin baguette slices (about 240 grams total)
• 240 grams grated Gruyère cheese (or Emmental / kashkaval)

Choosing ingredients and substitutes

Grated kashkaval or Emmental, in the same weight, work in place of Gruyère and give a slightly different flavor. You can use homemade broth; there’s no need for a ready-made imported one. Vegetable broth works for a milder version. The wine can be replaced with 150 ml of broth, and instead of a tablespoon of wine vinegar you can use two teaspoons of cider vinegar, adding it to taste.

Method

1. Slice thin and even. Onions sliced to uneven thickness caramelize at an uneven rate — some will burn before the rest turns golden.
2. Start caramelizing. Melt the butter with the oil in a heavy, wide pot, add all the onions and the half teaspoon of salt, and stir to coat. Cover and cook for 10 minutes over medium heat — the onions release water and shrink.
3. Uncover and caramelize for 35-40 minutes over medium-low heat. This is the whole soup. Stir only every 5-7 minutes, scraping the brown layer off the bottom each time. After 20 minutes you can add the teaspoon of sugar. The onions should reach a deep amber-brown, not a light gold.
4. Add garlic and flour. Add the garlic, stir for a minute, sprinkle in the flour and stir for another minute.
5. Pour in the wine and scrape. Add the wine, bring to a boil and scrape the bottom thoroughly. Cook for 3-4 minutes until most of the alcohol has evaporated.
6. Cook the soup. Add the broth, bay leaves and thyme, bring to a gentle boil and cook for 30 minutes over low heat. Finish with a tablespoon of wine vinegar or brandy, and adjust the salt and pepper.
7. Make the croutons. Toast the baguette slices in the oven at 180 degrees Celsius (356°F) until dry and crisp. A moist slice will disintegrate into the soup within a minute.
8. Divide and gratinate. Divide the soup among heatproof bowls, lay two slices on each and sprinkle with 40 grams of cheese. Put under the oven broiler for 2-4 minutes, until the cheese melts and browns in spots. Serve immediately — the bowl is scorching.

Nutrition facts and calorie estimate

The recommended serving is a bowl of about 300 ml, one-sixth of the recipe, with two baguette slices and 40 grams of cheese.

This is the only soup in the category where the garnish is bigger than the dish. The breakdown:

So the meaningful decision here isn’t about the soup but about the topping: one slice instead of two and 25 grams of cheese instead of 40 bring the serving down to about 380 calories, and soup with no topping at all comes to about 210 — in the range of an ordinary vegetable soup.

Sodium deserves no less attention than calories. Commercial beef broth and hard cheese are two concentrated sources of sodium, and one bowl can provide about half the recommended daily limit. More on the sodium page.

Variations and tips

• Vegan version: Olive oil instead of butter and a rich vegetable broth instead of beef broth. It’s worth adding a teaspoon of miso or a tablespoon of soy sauce at the end, to make up for the umami the broth provided.
• Without alcohol: Replace the wine with 150 ml of broth plus a tablespoon of white wine vinegar. The acidity is what the wine really contributes.
• Without heatproof bowls: Gratinate the bread slices with the cheese separately on a baking sheet, and lay them on the soup when serving. The result is almost identical.
• Making ahead: The onion soup itself improves a lot on the second day, keeps 4 days in the fridge and 3 months frozen. Always do the gratin just before serving.
• The right onion: Ordinary yellow onion is the classic choice. Sweet onion caramelizes faster but gives a sweetish soup, and red onion loses its color completely.

Summary

French onion soup is a recipe of patience: 45 minutes of caramelizing over moderate heat, little stirring, and scraping the bottom at every stage. Nutritionally it is the clearest case on the site of a dish whose topping is bigger than it is — about 210 calories in the soup and about 270 in the bread and cheese on top. For more soups see Soups, and for the nutritional values of the vegetable everything is built on — onion.