Classic French Onion Soup with Gruyère Toast

Why You’ll Love This Recipe

• Restaurant-worthy flavor at home: deeply caramelized onions and a splash of sherry build luxurious depth.
• Flexible base: choose beef stock for classic richness or vegetable stock for a satisfying vegetarian option.
• Crisp-meets-gooey topping: a thick baguette slice with blanket of broiled Gruyère turns each bowl into comfort in a crock.
• Make-ahead friendly: caramelize onions in advance, then finish the soup whenever you’re ready.

Grocery List

• Produce: 3 lb sweet onions, 2 garlic cloves, fresh thyme, bay leaves
• Dairy: Unsalted butter, Gruyère cheese (6 oz)
• Pantry: Olive oil, kosher salt, black pepper, dry sherry, low-sodium beef or vegetable stock, Worcestershire or soy/tamari, baguette, sugar, baking soda (optional)

Full Ingredients

For the soup

• 3 lb sweet onions (Vidalia or yellow), halved root-to-tip and thinly sliced
• 3 tbsp unsalted butter
• 1 tbsp extra-virgin olive oil
• 1 tsp kosher salt, plus more to taste
• 1/2 tsp granulated sugar (optional, encourages browning)
• 1/8 tsp baking soda (optional, speeds caramelization; see Pro Tips)
• 2 garlic cloves, minced
• 1/3 cup dry sherry, plus 1 tbsp to finish (optional)
• 6 cups low-sodium beef stock or rich vegetable stock
• 4 fresh thyme sprigs (or 1/2 tsp dried thyme)
• 2 bay leaves
• 2 tsp Worcestershire sauce (optional; omit for vegetarian) or 1 tsp soy sauce/tamari
• Freshly ground black pepper, to taste

For the cheesy toasts

• 6 slices baguette, 3/4-inch thick
• 1 tbsp olive oil or melted butter, for brushing
• 6 oz Gruyère cheese, coarsely grated (about 1 1/2 cups)

Step-by-Step Instructions

Step 1: Slice the onions and set up your pot

Use a heavy-bottomed Dutch oven or wide soup pot (5–6 quarts). Halve the onions root-to-tip so they hold together, then slice thinly into half-moons. The wide surface area of a Dutch oven encourages even browning.

Step 2: Slowly caramelize the onions

Melt the butter with the olive oil over medium heat. Add the onions, 1 teaspoon salt, the sugar, and baking soda (if using). Cook, stirring every few minutes, until onions release liquid and soften, about 10–15 minutes. Reduce heat to medium-low and continue cooking 35–45 minutes, stirring occasionally and scraping the bottom. If browning spots develop, splash in 1–2 tablespoons water and scrape to dissolve the fond. The onions are ready when jammy, mahogany-brown, and reduced by more than half.

Step 3: Add garlic and deglaze with sherry

Stir in the minced garlic and cook 1 minute until fragrant. Pour in 1/3 cup dry sherry and increase heat to medium. Scrape up all browned bits and cook until the sherry is mostly evaporated, 2–3 minutes. This deepens the flavor and adds a subtle nuttiness.

Step 4: Build and simmer the soup

Add the stock, thyme, bay leaves, and Worcestershire or soy (if using). Bring to a gentle simmer, then cook uncovered 20–25 minutes to meld flavors. Remove thyme stems and bay leaves. Taste and adjust seasoning with more salt and black pepper. For extra roundness, swirl in the final 1 tablespoon sherry.

Step 5: Toast the baguette

About 15 minutes before the soup is done, heat the oven to 400°F. Arrange baguette slices on a baking sheet, brush both sides with olive oil or butter, and toast 8–10 minutes, flipping once, until dry and crisp. This keeps the bread from turning soggy under the cheese.

Step 6: Top with Gruyère and broil

Heat the broiler to high and set a rack 6 inches from the element. Ladle hot soup into 6 broiler-safe crocks or ramekins on a rimmed sheet. Top each with a toast and a generous mound of Gruyère. Broil 2–4 minutes, watching closely, until the cheese is melted, bubbling, and browned in spots.

Step 7: Finish and serve

Let the crocks rest 1–2 minutes (they’re very hot). Crack black pepper over the cheese and garnish with small thyme leaves if you like. Serve immediately, taking care with the hot bowls.

Pro Tips

• Use a wide, heavy pot: more surface area means better evaporation and more even caramelization.
• Control the heat: if onions start to scorch, lower the heat and deglaze with a splash of water to save the fond.
• Optional baking soda speeds browning but can soften onions more quickly—use sparingly (1/8 tsp) for sweetest results without mushiness.
• Low-sodium stock gives you control; you can always add salt or a few drops of soy/tamari for umami at the end.
• Broiler safety: only use broiler-safe crocks; if unsure, broil bread and cheese separately on a sheet pan and float onto hot soup.

Variations

• Vegetarian and robust: use mushroom or roasted vegetable stock and finish with 1 tsp soy/tamari for depth.
• Cheese blend: swap in part Comté or Emmental for a classic Alpine flavor and extra meltability.
• Gluten-free: use sturdy gluten-free baguette or toasted rounds; everything else stays the same.

Storage & Make-Ahead

Caramelize onions up to 4 days ahead; refrigerate in an airtight container or freeze for up to 2 months. Finished soup (without bread and cheese) keeps 4 days in the fridge or 2 months in the freezer. Reheat gently until steaming. Toast bread and broil with cheese just before serving for best texture.

Nutrition (per serving)

Approximate values (with beef stock, one baguette slice, and Gruyère): 390 calories; 18g fat; 33g carbohydrates; 18g protein; 4g sugar; 2g fiber; 1050mg sodium.