Classic French Onion Soup Recipe: Step-by-Step Guide

French onion soup is made by slowly caramelizing onions until deeply golden, deglazing with wine, adding rich beef broth, and topping with toasted bread and melted Gruyère cheese. The entire process takes 1.5-2 hours with 20 minutes of active preparation.

Creating authentic French onion soup requires patience during the caramelization process and quality ingredients. This beloved French bistro classic transforms humble onions into a rich, savory delight through careful technique. While seemingly simple, mastering the proper caramelization method separates good soup from extraordinary soup.

Essential Ingredients for Authentic French Onion Soup

The magic of French onion soup comes from just a few high-quality components. Don't compromise on these key elements:

Ingredient	Quantity	Professional Recommendation
Yellow onions	4 lbs (about 6 large)	Use yellow onions for perfect balance of sweetness and pungency
Butter	4 tablespoons	Unsalted European-style butter for richer flavor
Olive oil	2 tablespoons	Combination with butter prevents burning during long cooking
Dry white wine	1 cup	Dry vermouth or Sauvignon Blanc works best for deglazing
Beef broth	6 cups	Homemade or low-sodium quality store-bought broth
Baguette	1 small loaf	Slightly stale bread provides ideal texture for topping
Gruyère cheese	1.5 cups shredded	Authentic choice that melts beautifully and adds nutty flavor
Thyme	2 sprigs	Fresh preferred, but 1 teaspoon dried works in a pinch

Step-by-Step French Onion Soup Preparation

Onion Caramelization: The Critical Foundation

Caramelizing onions properly makes or breaks your French onion soup. This isn't quick sautéing—it's a slow transformation:

Peel and thinly slice 4 pounds of yellow onions (about 6 large). Uniform 1/8-inch slices ensure even cooking.
Heat 4 tablespoons butter and 2 tablespoons olive oil in a heavy-bottomed Dutch oven over medium heat.
Add onions and stir to coat with fat. Season with 1 teaspoon salt to draw out moisture.
Reduce heat to medium-low and cook for 45-60 minutes, stirring every 5-7 minutes. Resist the urge to rush this step—proper caramelization develops complex flavors.
When onions reach a deep, rich mahogany color (not just golden), they're ready for the next step.

Building Flavor Layers

Boost the fond by adding 2 minced garlic cloves and cooking for 1 minute until fragrant.
Pour in 1 cup dry white wine to deglaze, scraping the browned bits from the bottom of the pot.
Simmer until wine completely reduces, about 5 minutes.
Add 6 cups quality beef broth, 2 thyme sprigs, and 2 bay leaves. Bring to a gentle simmer.
Cover and cook for 30 minutes to allow flavors to meld.

Perfecting the Soup Topping

While soup simmers, preheat oven broiler and slice baguette into 1/2-inch thick pieces.
Toast bread slices until golden on both sides (about 5 minutes at 350°F).
Ladle soup into oven-safe bowls, filling about 3/4 full.
Place 1-2 toasted bread slices on each bowl of soup.
Cover bread generously with shredded Gruyère cheese.
Broach under preheated broiler until cheese bubbles and develops golden spots (2-4 minutes).
Let rest 5 minutes before serving—this allows cheese to set slightly for perfect presentation.

Professional Tips for Exceptional French Onion Soup

Master French onion soup with these chef-recommended techniques that transform good soup into extraordinary:

Patience with caramelization: Rushing creates bitter, unevenly cooked onions. True caramelization takes 45-60 minutes at medium-low heat.
Balanced sweetness: If onions become too sweet, add a splash of sherry vinegar during the last 10 minutes of simmering.
Broth selection matters: For authentic French onion soup, use rich beef broth rather than chicken or vegetable alternatives.
Cheese alternatives: While Gruyère is traditional, Emmental or Comté provide similar melting properties and nutty flavor.
Salt timing: Adding salt early draws out onion moisture, speeding the initial cooking phase before true caramelization begins.

Avoiding Common French Onion Soup Mistakes

Even experienced cooks make these preventable errors when preparing traditional French onion soup:

Using high heat for caramelization: This burns onions rather than caramelizing them. Medium-low is essential.
Skipping the wine deglaze: Wine lifts the flavorful fond from the pot bottom, creating depth you can't achieve otherwise.
Overfilling soup bowls: Leave at least 1 inch space below the rim to prevent bubbling over when adding hot cheese topping.
Using pre-shredded cheese: These contain anti-caking agents that prevent proper melting. Always shred your own Gruyère.
Serving immediately after broiling: Letting the soup rest 5 minutes allows the cheese to set slightly for cleaner presentation.

Serving Suggestions and Variations

While classic French onion soup stands beautifully on its own, these thoughtful touches enhance the experience:

Pair with a simple green salad dressed in vinaigrette for a complete bistro-style meal
Add a splash of cognac to the wine deglaze for extra complexity
For vegetarian French onion soup, use mushroom broth and omit wine or substitute with dry sherry
Enhance presentation by floating a small fresh thyme sprig on each serving
Traditional French onion soup uses Gruyère, but adding 25% Parmesan creates a more complex flavor profile

Storage and Reheating Instructions

French onion soup actually improves in flavor after 24 hours as flavors continue to meld:

Cool soup completely before storing in airtight containers
Refrigerate for up to 4 days or freeze for up to 3 months
Reheat gently on stove over medium-low heat—avoid boiling which can make broth bitter
For best results, reheat soup base separately from toppings and add fresh cheese when serving
Never freeze soup with bread and cheese topping—always add these fresh when serving

Frequently Asked Questions

What type of onions work best for French onion soup?

Yellow onions provide the ideal balance of sweetness and pungency for authentic French onion soup. While some recipes suggest using sweet onions like Vidalias, professional chefs prefer yellow onions for their more complex flavor profile that develops beautifully during caramelization. Avoid red onions as they can impart an unwanted color and sharper taste.

How long should I caramelize onions for French onion soup?

Proper caramelization takes 45-60 minutes over medium-low heat. The onions should transform from white to a deep, rich mahogany brown—not just golden. Rushing this process creates bitter flavors rather than the complex sweetness that defines exceptional French onion soup. Stir every 5-7 minutes to ensure even cooking without burning.

Can I make French onion soup without alcohol?

Yes, you can make French onion soup without alcohol by substituting the wine with additional broth and a splash of apple cider vinegar or sherry vinegar. The vinegar provides the necessary acidity to balance flavors. However, the wine deglaze step serves an important purpose in lifting the flavorful fond from the pot bottom, so don't skip the deglazing process entirely.

Why does my French onion soup taste bitter?

Bitterness usually comes from burning the onions during caramelization. This happens when heat is too high or stirring is infrequent. If your soup tastes bitter, try adding a small pinch of sugar and a splash of sherry vinegar to balance the flavors. For future batches, maintain medium-low heat and stir regularly during the caramelization process.

What bread works best for French onion soup topping?

A day-old baguette provides the ideal texture for French onion soup topping. The slightly stale bread holds up better under the hot broth and melted cheese without becoming soggy. Avoid soft sandwich breads which disintegrate. For authentic results, use a traditional French baguette sliced 1/2-inch thick and toasted until crisp before adding to the soup.