Cheesy French Onion Soup

Key Ingredients and Substitutions

To make this delicious French onion soup you really only need a shortlist of easy-to-find ingredients, most of which you probably already have in your pantry or refrigerator.

• Onions are the star of this dish and we have an entire blog post dedicated to selecting and then caramelizing onions. You can use any onion but just note there will be differing levels of sweetness from the chosen variety. White onions will be sweet and mild. Red onions stronger onion flavor, are slightly bitter, and not as sweet. Yellow onions are our favorite French Onion soup. They are nice and mild with a naturally occurring sweetness you want for caramelized onions.
• Butter & Olive Oil are our go-to choices of fat for this recipe but you can substitute the olive oil for just butter. We always use and recommend unsalted butter so that you are only adding the amount of salt you want or the recipe calls for.
• Beef stock is the classic base but you can easily switch it out for vegetable stock to make this a vegetarian version. Chicken stock will also work if that is all you have on hand. As with any substitution, the final flavor will be different but still delicious.
• Dry Vermouth adds an earthy, herbal flavor to the soup and is completely optional. You can add a tablespoon of Worcestershire to give it some additional depth of flavor instead.
• Thyme sprigs and bay leaf are the only two “herbs” that you need for this recipe. We prefer to use fresh thyme sprigs but you can substitute with ground thyme. Typically one large sprig of thyme is equivalent to 1/4 teaspoon of dry thyme.
• French baguette is the classic bread of choice for this recipe but any bread that has a crispy crust can be used.
• Cheese is the final key ingredient. We use a combo of Gruyere and Emmentaler which are both types of Swiss cheeses. Gruyere is slightly less fatty than Emmentaler, which is why we use a combo, but you can use any type of Swiss cheese. The key is selecting a cheese that melts easily without breaking into liquid fat and milk solids.

How to Make French Onion Soup

Here are the quick step-by-step instructions with visuals; you can find the full instructions with the exact ingredients in the recipe card below.
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Pro-tip: Make a little extra soup as it freezes well. Defrost and top with some toasted slices of your favorite crusty bread and cheese for an easy weeknight soup dinner.

Caramelizing Onions

1. Prep and Soften the Onions: Rough chop onions so that slices are between ⅛ and ¼ inches thick. Heat the butter and olive oil in a saucepan on medium heat. Once the butter has melted add onions and sweat them until they become translucent.

2. Caramelize the Onions: Reduce heat to low and continue to cook onions, stirring every 5-10 minutes to prevent them from sticking. Deglaze pan with water or chicken stock when fond starts to form on the pan. As the onions further caramelize, continue stirring every 5-10 minutes and deglazing the saucepan as fond forms. When the onions achieve a blonde color they are the perfect texture for French Onion Soup.

French Onion Soup

1. Prep the Soup: Once the onions have cooked, add 4 cups of beef broth, thyme, and bay leaf. Bring soup to a boil, and then reduce heat. Partially cover with a lid and simmer for 20 minutes. Season with salt to taste

2. Top with Bread and Cheese: Place 4 oven/broiler-safe soup bowls on a cookie or baking sheet. Fill each of the soup bowls with the soup and then top with two slices of French baguette and ½ cup of shredded cheese. Broil until the cheese is melted and begins to brown.

Frequently Asked Questions