French Onion Soup (Deeply Caramelized, Cheesy Crouton Top)

What Makes This Recipe Work

Salting the onions as soon as they hit the pot draws out their moisture so they soften before they brown, and the long cook is what turns all those onions into a few cups of dark, sweet, jammy flavor.

Ingredients for French Onion Soup (Deeply Caramelized, Cheesy Crouton Top)

• 4 tbsp (55 g) unsalted butter
• 3 lb (1.4 kg) yellow onions, thinly sliced
• 1 tsp salt
• 1/2 tsp sugar
• 1/2 cup (120 ml) dry white wine or dry sherry (optional)
• 6 cups (1.4 L) low-sodium beef broth
• 1 tsp fresh thyme leaves or 1/2 tsp dried thyme
• 1 bay leaf
• 6 slices French bread or baguette, about 1 inch thick
• 1 1/2 cups (170 g) grated Gruyere or Swiss cheese
• 1/2 cup (55 g) grated Parmesan
• 1 tbsp olive oil

How to Make French Onion Soup (Deeply Caramelized, Cheesy Crouton Top)

1. Melt the butter in a large heavy pot over medium heat, add the onions and salt, and stir until they are coated.
2. Cook 20 minutes, stirring every few minutes, until the onions have wilted and released their liquid.
3. Continue cooking 20 minutes more, stirring often, until the onions are deep golden brown and sticky, about 40 minutes of browning in total.
4. Pour in the wine to deglaze, scrape up the browned bits, and cook until it is nearly evaporated, about 2 minutes.
5. Add the beef broth, thyme, and bay leaf, simmer partially covered 15 to 20 minutes, then taste and adjust the salt.
6. Meanwhile, heat the broiler and brush the bread slices with olive oil; toast until golden at the edges, 2 to 3 minutes.
7. Ladle the soup into oven-safe broiler bowls to about two-thirds full, float a slice of bread on each, and pile on the Gruyere and Parmesan.
8. Broil 2 to 4 minutes until the cheese is bubbling and browned in spots, then serve immediately.

Tips for the Best French Onion Soup (Deeply Caramelized, Cheesy Crouton Top)

• Do not rush the onions: about 20 minutes to wilt and 40 minutes to brown deeply is the timeline that builds the flavor.
• Slice the onions evenly so they brown at the same rate, and scrape the bottom of the pot when browned bits stick.
• Beef broth gives the darkest color and deepest flavor; low-sodium broth lets you control the salt.
• Set the filled bowls on a sheet pan before broiling so drips land on the pan, not the oven floor.

Variations and Substitutions

• Slow cooker French onion soup: caramelize the onions on the stovetop as directed, then transfer them to the slow cooker with the broth and cook on low 6 to 8 hours; ladle into bowls and broil the cheese topping just before serving.
• For chicken French onion soup, use chicken broth and add shredded cooked chicken under the bread before the cheese.
• Vegetable broth makes a meatless version with the same caramelized onion base.
• Sourdough bread gives a sturdier cap that holds up to the broth longer than baguette.

How to Store and Reheat

• Refrigerate the soup base without the bread and cheese for up to 5 days, then reheat and add the topping.
• The caramelized onion base freezes for up to 3 months; thaw it overnight before reheating.

French Onion Soup (Deeply Caramelized, Cheesy Crouton Top) FAQ