French Onion Soup

Bubbling Gruyere cheese and crispy baguette top a brothy base full of evenly braised onions in this showstopping yet simple French onion soup recipe. Whether you’re making it to warm up on a cold day or for a rich date night in, this tastes rich, luxurious, and cozy each and every time.

Read on for ingredient tips, a slow cooker version, and make-ahead instructions!

A must-order every time we go to a nice restaurant, we will never turn down French onion soup. There is something about the look of a beautifully bubbling load of cheese, browned to perfection over crisp bread.

If you’ve ever thought that it would be too difficult to make at home, we're here to tell you that it is TOTALLY doable and you will be absolutely enamored with the results.

And the aroma in the kitchen? Oh man! Let’s get started!

What is French onion soup, exactly?

Onion soups have been around since Roman times, as onions were straightforward to grow in many climates for little. The version of French Onion soup that we are used to here in the U.S. originated in the 1800s. In the 1860s, a New York restaurateur brought the recipe to the U.S., and it was originally served with a crispy crouton. It is known for its base of rich, buttery broth packed with caramelized or braised yellow onions. The topping of crispy bread and melted cheese is an absolute must!

This style can sometimes get confused with standard onion soup; the British version has yellow, red, and white onions along with shallots and fennel. You may also find it with various types of broths and usually has sage included.

How to Make French Onion Soup From Scratch

1. Braise the Onions – This is a lengthy process, but almost completely hands-off. First, you’ll cook the onions in a heavy pot in the oven uncovered for 1 hour. Give it a stir, then do another until with a lid slightly ajar. After another stir, they’ll get an additional 30 to 45 minutes.
2. Finish Onions on Stovetop – After braising, the onions get put on the stove, deglazed a few times, and the caramelization is complete!
3. Add Remaining Soup Ingredients – Broth, water, thyme, and a bay leaf get added to the onions and simmered for 30 minutes, then seasoned with salt and pepper.
4. Broil & Serve! – Ladle the soup into oven-safe crocks, top wtih baguette slices and sprinkle with cheese. Broil until the cheese is melted and bubbly. Dig in!

How to Make French Onion Soup in the Slow Cooker

While it will not be quite as rich and flavor-packed, it will still be rich! Here is what to do:

1. Combine the butter and onions in a large skillet over medium-low heat until golden and caramelized, about 20 minutes.
2. Add the onions and the remaining ingredients (except for the bread and cheese) to the slow cooker and cook on low for 6 to 8 hours. We would recommend replacing the water with either chicken or beef stock to add a little more flavor since we aren’t doing the intense braising in this method.
3. Remove the bay leaf, and finish off the soup as directed in this recipe (ladling into bowls and topping with the bread and cheese, then broiling).

Keeping leftovers

• Make-Ahead: For a standby flavor, make the soup a day or 2 in advance. Alternatively, the onions can be prepared through step 1, cooled in the pot, and refrigerated for up to 3 days before proceeding with the recipe.
• Storage: Leftover soup can be refrigerated for up to 4 days.
• Freezing: The soup can be frozen in an airtight container for up to 3 months. Do not freeze the cheese-covered bread with the soup; freeze the soup separately and add the bread and cheese before serving.

• Yield: 6 servings
• Prep: 15 minutes
• Cook: 4 hours 30 minutes
• Total: 4 hours 45 minutes

Ingredients

Soup:

• 3 tablespoons unsalted butter, cut into 3 pieces
• 6 large yellow onions, about 4 pounds, halved and cut into ¼-inch thick slices
• Table salt
• 2 cups ( 500 ml ) water, plus extra for deglazing
• ½ cup ( 120 ml ) dry sherry
• 4 cups ( 940 ml ) chicken broth
• 2 cups ( 480 ml ) beef broth
• 6 sprigs fresh thyme, tied with kitchen twine
• 1 bay leaf
• Ground black pepper

Cheese Croutons:

• 1 small baguette, cut into ½-inch slices
• 8 ounces ( 226.8 g ) shredded Gruyere cheese, about 2½ cups

Method

1. Braise/Caramelize Onions: Adjust oven rack to lower-middle position and heat oven to 400 degrees F. Generously spray inside of heavy-bottomed large (at least 7-quart) Dutch oven with nonstick cooking spray. Place butter in the pot and add onions and 1 teaspoon salt. Cook, covered, 1 hour (onions will be plush and slightly reduced in volume). Remove pot from oven and stir onions, scraping bottom and sides of pot. Return pot to oven with lid slightly ajar and continue to cook until onions are soft and golden brown, 1½ to 1¾ hours longer, stirring onions and scraping bottom and sides of pot after 1 hour.
2. Carefully remove pot from oven and place over medium-high heat. Using oven mitts to handle pot, cook onions, stirring frequently and scraping bottom and sides of pot, until liquid evaporates and onions brown, 15 to 20 minutes, reducing heat to medium if onions are browning too quickly. Continue to cook, stirring frequently, until pot bottom is coated with dark crust, 6 to 8 minutes, adjusting heat if necessary. (Scrape any crust that collected on spoon back into onions.) Stir in ¼ cup water, scraping pot bottom to loosen crust, and cook until water evaporates and pot bottom has formed another dark crust, 6 to 8 minutes. Repeat process of deglazing 2 or 3 more times, until onions are dark brown. Stir in sherry and cook, stirring frequently, until sherry evaporates, about 5 minutes.
3. Finish the Soup: Stir in broths, 2 cups water, thyme, bay leaf, and ½ teaspoon salt, scraping up any final bits of browned crust on bottom and sides of pot. Increase heat to high and bring to simmer. Reduce heat to low, cover, and simmer 30 minutes. Remove and discard herbs, then season with salt and pepper.
4. Broil with Cheesy Baguette Slices: While soup simmers, arrange baguette slices in single layer on baking sheet and bake in 400-degree oven until bread is dry, crisp, and golden at edges, about 10 minutes. Set aside.
5. Adjust oven rack 6 inches from broiler element and heat broiler. Set individual broiler-safe crocks on baking sheet and fill each with about 1¾ cups soup. Top each bowl with 1 or 2 baguette slices (do not overlap slices) and sprinkle evenly with Gruyere. Broil until cheese is melted and bubbly around edges, 3 to 5 minutes. Let cool 5 minutes before serving.

Notes

Equipment: 7-quart Dutch oven / Broiler-safe soup crocks

Onions: Use yellow onions for a standby balance of flavor.

Broth: This recipe calls for a combination of beef and chicken broth; you can adjust the ratios based on what you have on hand and substitute stock if you’d like.

Baguette: Sliced French baguette is the traditional topping for French onion soup, but any crusty bread will suffice, and if you’re in a pinch, you can use big croutons, too!

Cheese: Gruyere is the standard, but shredded Swiss makes a great substitute.

Broiling: If using ordinary soup bowls, sprinkle the toasted bread slices with Gruyère and return them to the broiler until the cheese melts, then float them on top of the soup.

Make-Ahead: For a standby flavor, make the soup a day or 2 in advance. Alternatively, the onions can be prepared through step 1, cooled in the pot, and refrigerated for up to 3 days before proceeding with the recipe.

Storage: Leftover soup can be refrigerated for up to 4 days.

Freezing: The soup can be frozen in an airtight container for up to 3 months. Do not freeze the cheese-covered bread with the soup; freeze the soup separately and add the bread and cheese before serving.

Recipe adapted from Cook’s Illustrated

Photography by Lauren Grant.