Why isn't my soup as dark as restaurant versions?

The color comes primarily from well-caramelized onions and quality beef broth. Patience with the onions is key—they should be a deep golden brown (but not burned). Some restaurants add kitchen bouquet or soy sauce for color, which you can try if desired.

Can I make this in a slow cooker or Instant Pot?

You can, but the onions won't caramelize the same way. For best results, caramelize the onions on the stovetop, then transfer to a slow cooker with the broth ingredients to simmer. The Instant Pot works well for the broth portion but not for properly caramelizing onions.

What if I don't have oven-safe soup bowls?

No problem! Toast the bread with cheese on top under the broiler separately, then float these cheesy toasts on your soup bowls. You'll get the same flavors without needing special bowls.

Why add horseradish? I've never seen that in French onion soup before.

Horseradish provides a subtle background note that enhances the beef flavor without adding detectable spiciness. It's a secret ingredient that adds complexity, but you can absolutely omit it if you prefer.

French Onion Soup Recipe

Name: French Onion Soup Recipe
Prep time: 10 min
Cook time: 1 h 40 min
Total time: 1 h 50 min
Cuisine: French
Ingredients: 4 large yellow onions (about 3 pounds), thinly sliced; 4 tablespoons butter (half stick); 1 tablespoon kosher salt (use less if using table salt); 1/4 teaspoon cayenne pepper (optional); 2 tablespoons all purpose flour; 1/2 cup sherry wine or white wine; 1 tablespoon fresh lemon juice (about half a lemon); 8 cups high quality beef broth; 2 cups water; 1 tablespoon Better Than Bouillon Beef Base; 3 carrots, peeled and roughly chopped; 1 yellow onion, roughly chopped; 2 stalks celery, roughly chopped; 6 large cloves garlic, smashed; 1 teaspoon prepared horseradish (or more, to taste); 3 sprigs fresh thyme (or 1/2 teaspoon dried thyme); 3 small sprigs fresh rosemary (or 1/2 teaspoon dried rosemary); 3 bay leaves; 15 peppercorns (about 1/2 teaspoon); 1 (1-pound) loaf of French bread, sliced into 1-inch thick slices; 1 cup gruyere cheese, freshly grated; 1 cup parmesan cheese, freshly grated; 8 ounces Swiss cheese, sliced; Freshly chopped chives; Freshly cracked black pepper

Description

French Onion Soup is a classic French recipe featuring deeply caramelized onions simmered in a rich, flavorful homemade beef broth. Topped with crisp toasted French bread and a melty combination of Gruyere, Swiss, and Parmesan cheeses, this soup is broiled to perfection for a comforting and savory meal.

Ingredients

Units Scale

For the Onion Soup Base

4 large yellow onions (about 3 pounds), thinly sliced
4 tablespoons butter (half stick)
1 tablespoon kosher salt (use less if using table salt)
1/4 teaspoon cayenne pepper (optional)
2 tablespoons all purpose flour
1/2 cup sherry wine or white wine
1 tablespoon fresh lemon juice (about half a lemon)

For the Broth

8 cups high quality beef broth
2 cups water
1 tablespoon Better Than Bouillon Beef Base
3 carrots, peeled and roughly chopped
1 yellow onion, roughly chopped
2 stalks celery, roughly chopped
6 large cloves garlic, smashed
1 teaspoon prepared horseradish (or more, to taste)
3 sprigs fresh thyme (or 1/2 teaspoon dried thyme)
3 small sprigs fresh rosemary (or 1/2 teaspoon dried rosemary)
3 bay leaves
15 peppercorns (about 1/2 teaspoon)

For the Topping

1 (1-pound) loaf of French bread, sliced into 1-inch thick slices
1 cup gruyere cheese, freshly grated
1 cup parmesan cheese, freshly grated
8 ounces Swiss cheese, sliced

Garnish (optional)

Freshly chopped chives
Freshly cracked black pepper

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Instructions

Slice the Onions – Thinly slice about 4 large yellow onions (about 3 pounds) to yield about 8 cups. This ensures even caramelization and makes the soup easier to eat.
Caramelize the Onions – In a 12-inch, high-sided stainless steel pan, melt 4 tablespoons butter over medium heat. Add the onions, sprinkle with 1 tablespoon kosher salt, and add the cayenne pepper. Cook over medium heat for 10 minutes until onions are translucent, stirring occasionally.
Slow Caramelization – Reduce heat to medium-low, and continue to cook the onions for about 90 minutes, stirring every 10-20 minutes, until they are deeply golden and sweet, with no oniony ‘bite’, ensuring not to scorch the edges.
Prepare the Broth – In a large Dutch oven or stockpot over high heat, combine 8 cups beef broth, 2 cups water, and 1 tablespoon Better Than Bouillon Beef Base. Add carrots, onion, celery, garlic, horseradish, thyme, rosemary, bay leaves, and peppercorns. Bring to a boil, then reduce heat and simmer, covered (with steam vent), while onions caramelize.
Strain the Broth – Once the onions are caramelized and the broth has simmered (about 90 minutes), strain the broth through a colander, discard the solids (veggies and herbs), and return the broth to the pot to keep it warm.
Add Flour and Deglaze – Sprinkle the caramelized onions with flour, stirring and cooking for 1-2 minutes to remove any raw flour taste. Add sherry or white wine, increase heat to medium, and deglaze the pan, scraping up all browned bits. Add lemon juice and continue to cook until most liquid is absorbed.
Combine Onions and Broth – Transfer the onions and any pan juices to the warm broth. Stir well, taste and adjust seasoning, adding more salt, horseradish, or herbs as needed.
Prepare the Bread – Preheat oven to 350°F. Slice French bread into 1-inch slices. Arrange slices in a single layer on a baking sheet and toast in the oven for 10 minutes. Flip and toast another 5 minutes until both sides are crisp. Optionally, butter the slices before toasting for extra richness.
Assemble the Soup – Grate Gruyere and Parmesan cheese. Place about 1/2 tablespoon of each cheese in the bottom of 7 oven-safe bowls. Ladle soup into bowls, top each with a toasted bread slice, sprinkle with more Gruyere and Parmesan, and top with a slice of Swiss cheese.
Broil and Serve – Place bowls on a baking sheet and transfer to the oven on a rack set in the upper third. Broil on high for 2–4 minutes, until cheese is melted and browned in spots. Remove carefully, garnish with chives and black pepper, and serve hot. Warn guests that bowls will be very hot.

Notes

For a vegetarian version, substitute beef broth with a rich vegetable broth.
Butter each bread slice before toasting for extra flavor.
Keep bread and cheese separate from soup for storage and when freezing.
Fresh herbs provide superior flavor but dried herbs can be used in a pinch.
Broil soup in oven-safe bowls only; take care as bowls become very hot during broiling.
Soup stores well in the refrigerator for 4-5 days or can be frozen (leave bread and cheese out until serving).

Nutrition

Serving Size: 1 bowl (about 2 cups)
Calories: 410
Sugar: 8 g
Sodium: 1450 mg
Fat: 22 g
Saturated Fat: 12 g
Unsaturated Fat: 8 g
Trans Fat: 0.5 g
Carbohydrates: 35 g
Fiber: 4 g
Protein: 19 g
Cholesterol: 55 mg