Bistro French onion soup is a bowl of sweet, soft, caramelized onions in a flavorful beef broth topped with gooey cheese melting into toasted slices of French bread. While our recipe is easy, good things take time – whether it’s this soup recipe, our caramelized onion and goat cheese bites, or our turkey burger with mushrooms and onions. You’ll find it is worth every spoonful, however.
Key Ingredients and Substitutions
To make this delicious bistro French onion soup, you 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 that the chosen variety will have differing levels of sweetness. White onions will be sweet and mild. Red onions have a stronger onion flavor, are slightly bitter, and are 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 and Olive Oil are our go-to fat choices for this recipe, but you can substitute the olive oil for just butter. We always use and recommend unsalted butter so that you add only 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. Instead, you can add a tablespoon of Worcestershire to give it some additional depth of flavor.
- Thyme sprigs and bay leaf are the only two “herbs” needed 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 with a crispy crust can be used.
- Cheese is the final key ingredient. We use a combo of Gruyere and Emmentaler, which are both Swiss cheeses. Gruyere is slightly less fatty than Emmentaler, so we use a combo, but you can use any Swiss cheese. The key is selecting a cheese that melts easily without breaking into liquid fat and milk solids.
How to Make Bistro 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 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 the heat to low and continue to cook the onions, stirring every 5-10 minutes to prevent them from sticking. Deglaze the 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 bowl 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
Yes! Once the soup has cooled, store it in a freezer-safe container or gallon-size freezer bag. Freeze bags are my preference since they can be placed flat in the freezer and stacked. The soup can be frozen for up to 3 months. When ready to reheat, just thaw it overnight in the refrigerator and then heat it in a saucepan on the stove until warmed through. Then top with sliced baguette and shredded cheese, and broil until cheese has melted.
Note: It is best to freeze soup before topping it with bread and cheese.
Yes! You can make the soup part of this recipe up to 2 days ahead. Refrigerate it in an airtight container until ready to use. When ready to serve, reheat it in a saucepan on the stove until warm. Top with baguette slices and shredded cheese, and broil until cheese has melted.
More Soup Recipes to Try
Looking for more inspired, comforting soup recipes? Try these other favorites:
- Italian Sausage Gnocchi Soup -This 30-minute one-pot soup is made from canned tomatoes, packaged gnocchi, and sausage and is the perfect weeknight meal.
- Pork Pozole Verde – This recipe is for traditional Mexican comfort food with a New Mexico twist. Made with grilled pork, tomatillo, and hatch peppers, it is a robust soup that borders on a stew.
- Rotisserie Chicken Tortilla Soup – Ready in 30 minutes, this soup is flavorful, quick, and perfect for leftovers. It’s made from tender rotisserie chicken, black beans, corn, and spices in a smoky tomato broth. Top with crispy tortillas and lime for a delicious weeknight dinner.
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Bistro French Onion Soup
This recipe may contain paid affiliate sales links. As an Amazon Associate, I earn from qualifying purchases. Please see my full disclaimer policy for details.
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Equipment
- Oven/Broiler-Safe Soup Bowls
Ingredients
Caramelized Onions
- 3 large peeled sweet or yellow onions, (about 1.5 pounds)
- 2 tablespoons olive oil
- 2 tablespoons unsalted butter
- 1 ½ cups water or beef stock
French Onion Soup
- 4 cups beef broth
- 2 tablespoon dry vermouth optional
- 4 springs thyme
- 1 bay leaf
- salt to taste
- 8 slices baguette approximately 1 inch thick
- 1 cup Gruyere cheese shredded
- 1 cup Emmentaler cheese shredded
Instructions
Caramelized 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.
- Reduce heat to low and continue to cook onions, stirring every 5-10 minutes to prevent them from sticking. Deglaze pan with water or stock when fond starts to form on the pan.
- As onions continue to caramelize, continue stirring every 5-10 minutes and deglazing the saucepan as fond forms.
- Continue cooking until onions have reached a deep blonde color.
French Onion Soup
- Once onions have cooked, add 4 cups of beef broth, dry vermouth, 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
- Combine Gruyere and Emmentaler cheese in a medium bowl, set aside.
- 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.