French onion soup recipe: the Paris bistro classic

This French onion soup recipe follows the Paris bistro version, soupe à l'oignon gratinée: onions browned slowly until they turn to jam, a beef broth sharpened with white wine, and a lid of toasted bread and Comté grilled until it blisters.

Onion soups are old and cheap, but the gratinée became a Paris institution in the market halls of Les Halles, where porters and night owls ate it before dawn. The whole dish rests on one step. Onions have no shortcut: the colour, and most of the flavour, comes from an hour in the pot.

Ingredients

There is no shortcut with onions: the colour and the flavour both take an hour.

• 1.2 kg yellow onions, halved and thinly sliced
• 50 g unsalted butter
• 1 tbsp neutral oil
• 1 tsp fine salt, plus more to taste
• 1 tbsp plain flour
• 150 ml dry white wine
• 1.2 litres beef stock
• 2 sprigs thyme and 1 bay leaf
• 1 tbsp cognac (optional)
• Freshly ground black pepper
• 8 slices day-old baguette, 1 cm thick
• 200 g Comté or Gruyère, coarsely grated

Method

1. Melt the butter with the oil in a wide, heavy pot over medium heat, add the onions and salt. Salt draws out water, so the onions soften before they colour, and a wide pot lets the steam escape.
2. Cook for 45 to 60 minutes, stirring every few minutes and lowering the heat as they darken, until deep amber and soft. If the base catches, add a spoonful of water and scrape: that brown layer is flavour, not a mistake.
3. Sprinkle in the flour and stir for 2 minutes. It cooks out the raw taste and gives the broth a little body.
4. Pour in the wine and reduce by half, scraping the bottom. Its acidity balances the sweetness of the onions.
5. Add the stock, thyme and bay and simmer uncovered for 30 minutes. Season with pepper, salt and the cognac at the end, when the broth has reduced.
6. Meanwhile, dry the bread in a 180°C oven for 10 minutes. Dry croutons hold up under the cheese instead of dissolving.
7. Heat the grill. Ladle the soup into ovenproof bowls, float two croutons in each, heap the cheese right to the rims and grill for 3 to 5 minutes until bubbling and browned.

How to get the gratinée right

The stock matters as much as the onions: a good homemade or butcher's stock gives depth that cubes cannot. Cheese touching the rim sticks to the bowl and forms the crust, so do not be shy. A dry white from Jura or Alsace suits the table. For another Paris classic, try our Mont Blanc chestnut dessert.

French onion soup: your questions

Which onions work best? Yellow onions. Sweet onions brown quickly but taste flat, and red onions turn a dull grey in the broth.

Can I make it ahead? Yes. The soup keeps for three days in the fridge and freezes for three months; toast the bread and gratinate only when you serve it.

Can it be vegetarian? Use a dark vegetable or mushroom stock with a teaspoon of soy sauce for depth, and check that the cheese is made without animal rennet.