Soupe à l’Oignon Gratinée (French Onion Soup)

Deeply caramelized onions in a rich beefy broth, finished with toasted bread and a bubbling cap of Gruyère.

Ingredients

• 4 large yellow onions, thinly sliced (about 1.2 kg / 2.6 lb)
• 3 tbsp butter
• 1 tbsp olive oil
• 1 tsp kosher salt (plus more to taste)
• 1/2 tsp black pepper
• 2 tbsp all-purpose flour
• 1/2 cup dry white wine (or dry vermouth)
• 6 cups (1.5 L) beef stock (or half beef, half chicken stock)
• 2 sprigs fresh thyme (or 1/2 tsp dried thyme)
• 1 bay leaf
• 1 tsp Worcestershire sauce (optional but recommended)
• 8 slices baguette (or any sturdy bread), 1.5 cm / 1/2" thick
• 2 cups (200 g) grated Gruyère (or Comté)
• 30 g (1 oz) Parmesan, finely grated (optional but excellent)
• 1 garlic clove, cut in half (for rubbing toast)

Method

• 1

  Step 1: Caramelize the onions (the magic step)

  In a large heavy pot (Dutch oven ideal), melt butter with olive oil over medium heat. Add onions, salt, and pepper. Cook 10 minutes, stirring occasionally, until softened and reduced. Then lower heat to medium-low and cook 35–45 minutes, stirring every few minutes, scraping the bottom well, until onions are deep golden-brown and jammy (not just pale). If the pot looks like it’s catching, add a splash of water and scrape—those browned bits are flavor.

• 2

  Step 2: Build the base

  Sprinkle flour over the onions and stir constantly for 1 minute to cook out the raw flour. Add wine and stir, scraping up everything stuck to the bottom, until the wine is mostly evaporated and the onions look glossy, about 2–3 minutes.

• 3

  Step 3: Simmer the soup

  Add stock, thyme, bay leaf, and Worcestershire (if using). Bring to a gentle simmer, then cook uncovered 20–25 minutes to meld flavors. Taste and adjust salt and pepper. Remove thyme sprigs and bay leaf.

• 4

  Step 4: Toast the bread

  Heat oven to 200°C / 400°F. Arrange bread slices on a tray and toast 8–10 minutes, flipping once, until crisp and golden. Rub one side lightly with the cut garlic clove.

• 5

  Step 5: Gratiner (broil the cheese topping)

  Ladle hot soup into 4 oven-safe bowls/ramekins on a baking tray. Float 1–2 toasts on each bowl (garlic side down). Pile on Gruyère, then a little Parmesan if using. Broil/grill on high 2–4 minutes until the cheese is melted, bubbling, and spotted brown. Let stand 2 minutes (it’s lava-hot), then serve.

Tips

• **Onion color = soup flavor:** Don’t rush caramelizing; you’re aiming for deep amber onions. If needed, turn heat down and be patient—this is the whole point.
• **No wine?** Use a splash of apple cider vinegar (1–2 tsp) or extra stock; you’ll lose some complexity but it still works.
• **Stock choice:** Beef stock gives the classic bistro depth. If yours is very salty, hold back on salt until the end.
• **Bread matters:** Use sturdy bread so it doesn’t dissolve immediately; toast well so it stays afloat.
• **Make ahead:** Soup (without bread/cheese) keeps 4 days in the fridge or 3 months frozen. Reheat, then gratiner just before serving.
• **Serve with:** A simple green salad with a sharp vinaigrette (mustard, vinegar, olive oil) to cut through the richness.

Nutrition (per serving, estimate)