French Onion Soup (Soupe à l'Oignon Gratinée with Caramelized Onions and Gruyère Toast)

Soupe à l'oignon gratinée, the French onion soup of Paris bistros, is a deep brown broth built almost entirely from onions, topped with toasted baguette and a blistered layer of melted Gruyère. It is one of the best things to cook once the evenings turn cold: onions are cheap and at their sweetest in autumn, the pot mostly looks after itself, and the finished bowl is hot, savory and filling enough to be dinner on its own.

Three things make this version work. First, a full kilo of yellow onions is cooked slowly in butter for a good 45 minutes, not 15, until they are soft, jammy and mahogany brown; that slow caramelization is where nearly all the flavor comes from, so there is no shortcut. Second, the pan is deglazed with dry white wine, which lifts the sticky browned bits off the bottom and adds a little brightness against the sweetness. Third, the toast is baked crisp and rubbed with garlic before it goes into the bowl, so it holds up under the cheese instead of dissolving into mush.

You will need oven-safe bowls or ramekins that can go under the broiler. If you do not have any, see the Tips section for an easy workaround.

Ingredients

• 1 kg (2.2 lb) yellow onions (about 5 to 6 medium), halved and sliced 3 mm (1/8 inch) thick
• 60 g (4 tablespoons) unsalted butter
• 1 tablespoon olive oil
• 1 teaspoon salt, plus more to taste
• 1 teaspoon sugar (optional, to help browning)
• 1 tablespoon all-purpose flour
• 150 ml (2/3 cup) dry white wine, or 60 ml (1/4 cup) brandy
• 1.2 liters (5 cups) beef stock, preferably homemade or low-sodium
• 2 sprigs fresh thyme (or 1/2 teaspoon dried)
• 1 bay leaf
• Freshly ground black pepper
• 8 slices baguette, cut 1.5 cm (2/3 inch) thick
• 1 garlic clove, peeled
• 150 g (5 oz) Gruyère cheese, coarsely grated (or Comté or Emmental)

Instructions

1. Peel and halve the onions through the root, then slice them from pole to pole about 3 mm thick. Even slices matter here: thin shreds burn while thick pieces stay pale.
2. Melt the butter with the olive oil in a heavy 4 to 5 liter pot or Dutch oven over medium heat. Add the onions and the salt, stir to coat, cover and cook for 10 minutes until the onions have wilted and released their liquid.
3. Uncover, lower the heat to medium-low and cook for 45 minutes, stirring every 5 minutes and scraping the browned film off the bottom each time. In the first 20 minutes the onions turn golden; after that they shrink, turn sticky and darken to a deep mahogany brown. If they start to catch, add a tablespoon of water and scrape. Stir in the sugar during the last 15 minutes if the color is slow to develop.
4. Sprinkle the flour over the onions and stir for 1 minute. Pour in the white wine and scrape the pot well; let it bubble for 2 to 3 minutes until the wine has almost completely cooked away.
5. Add the beef stock, thyme and bay leaf. Bring to a boil, then reduce to a gentle simmer and cook, partly covered, for 20 to 25 minutes so the flavors knit together. Fish out the thyme stems and bay leaf, then season with pepper and more salt if needed. The soup should taste deep and savory, not sweet.
6. While the soup simmers, heat the oven to 200°C (400°F). Lay the baguette slices on a baking sheet and bake for 8 to 10 minutes, turning once, until dry and golden. Rub one side of each slice with the garlic clove.
7. Switch the oven to the broiler (grill) setting and set a rack about 15 cm (6 inches) below the element. Place 4 oven-safe bowls on a baking sheet, ladle in the hot soup to about 2 cm below the rim, float 2 toasts on each and pile the grated Gruyère over the bread so it reaches the edges.
8. Broil for 3 to 5 minutes, until the cheese is melted, bubbling and browned in patches. Let the bowls stand for 2 minutes (the soup is scalding) and serve immediately.

Tips

• Do not rush the onions. Turning the heat up gives you burnt edges and pale, raw-tasting centers; 45 minutes at medium-low gives you sweet, uniformly brown onions. The whole pot should reduce to roughly a quarter of its starting volume.
• Substitutions: Comté or Emmental melt just as well as Gruyère, and a mix of Gruyère and a little Parmesan adds extra salt and crunch. Brandy or dry sherry can replace the wine. For a vegetarian soup, use a dark vegetable stock and add 1 tablespoon of soy sauce or 1 teaspoon of miso to make up for the missing beef depth.
• Make ahead: the soup base (through step 5) improves overnight. Keep it in the fridge for up to 4 days or freeze for up to 3 months, then reheat to a simmer and finish with fresh toast and cheese. Never freeze the assembled, gratinéed bowls.
• No oven-safe bowls? Top the toasted baguette slices with the cheese, broil them on the baking sheet until bubbling, then float them on the soup in ordinary bowls.
• Serve with a crisp green salad dressed with mustard vinaigrette and a glass of the same dry white wine you used in the pot. For a heartier meal, follow it with a simple steak or roast chicken.
• Good stock is half the soup. If you are using store-bought stock, choose a low-sodium one and taste before adding the final salt, as the cheese and toast add plenty on top.

Nutrition

Nutrition information is an estimate only: about 430 kcal, 18 g protein, 22 g fat, 38 g carbohydrate per serving (one bowl with two cheese toasts).