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If you didn’t know it, you’d never guess that this is Vegetarian French Onion Soup. One simple, umami-rich ingredient makes all the difference.

Vegetarian French Onion Soup served in traditional brown bowls with a long handle

Are you familiar with umami? It’s the Japanese term for the fifth primary flavor after sweet, sour, bitter and salty. It’s that essence that elevates a dish from okay to extraordinary and what makes this vegetarian version of the quintessential French soup taste just like the original. 

Ingredients You Need to Make Vegetarian French Onion Soup

vegetarian french onion soup ingredients on a white marble board.
  • Butter: Ideally high fat, European style butter, but any salted or unsalted butter you have on hand will work.
  • Onions: Yellow onions, sweet onions, or red onions all work well.
  • Bread: A crusty French bread or peasant bread with the crust removed, or cubed French baguette work well in this recipe.
  • Flour: white all-purpose flour
  • Thyme: dried thyme leaves or twice the amount of fresh thyme leaves
  • Wine: Any dry white wine will do. Be sure to choose one that you’d happily enjoy a glass of as the flavor will concentrate as it cooks down.
  • Broth: mushroom broth
  • Cognac: or brandy
  • Sugar: granulated white sugar
  • Cheese: Gruyère cheese or French Comté cheese (French Swiss-type cheese) or other Swiss Cheese
  • Kosher Salt and Freshly Ground Black Pepper

The Magic Ingredient

Lots of ingredients are packed with umami flavors, from tomatoes and Parmesan to miso paste and soy sauce. But in this vegetarian version of classic French onion soup, the umami comes from mushroom broth. If you’ve never cooked with it, trust me, you’ll fall in love with its depth of flavor.

Mushroom broth may seem like a curious choice, but here me out. When I tested this recipe with vegetable broth, the soup was good, but it lacked the flavor depth and complexity of the original. Without the meaty broth it was missing ‘something’. As in so many other savory dishes, a bit of umami was just the thing to add that little bit of flavor magic.

Why this tastes just like the traditional version.

The rest of the ingredients here are classic, based on my go-to French Onion Soup recipe adapted from Julia Child’s iconic book, Mastering the Art of French Cooking. Buttery sweet caramelized onions and earthy thyme simmer in white wine and flavorful broth then get spiked with a splash of cognac and finished with toasted bread and plenty of hot, bubbly cheese. So in most ways this is still a traditional French onion soup. It’s mainly the mushroom broth that’s different, as a substitute for the typical umami-rich beef stock.

Though this soup requires some time at the stove, the prep work is easy. And, for much of the cooking time the soup cooks itself low and slow in a Dutch oven. If you’ve been on the hunt for a vegetarian version of this quintessential French soup, I hope you’ll give this one a try.

FAQ

What are the best onions to use in French onion soup?

Yellow onions, sweet onions, or red onions are all good choices. You could also use a combination.

Can I make a vegan version of this French onion soup?

You sure can. Just use olive oil instead of butter and omit the cheese at the end (or top with a vegan cheese that’s suitable for melting under the broiler.)

Can I make vegetarian French onion soup without alcohol?

Yes, absolutely. Just substitute more mushroom broth for the white wine and skip the cognac.

More Delicious Vegetarian Soup Recipes

How to Make Vegetarian French Onion Soup

Add onion to melted butter in a large soup pot or Dutch oven and stir to coat. Cover and cook on low 15 minutes.

While the onion cooks, toast the bread cubes until crisp on a baking sheet in a 400˚F oven. Set aside.

Remove cover and add salt and sugar to onions. Increase heat to medium-low; cook and stir until the onions have caramelized to a deep, golden brown.

Stir flour into caramelized onions; cook and stir 3 minutes. Stir in thyme, wine, and mushroom broth. Bring to simmer and cook 30 to 40 minutes more. Remove from heat and stir in Cognac and kosher salt and pepper to taste.

Ladle soup into bowls (broiler-safe)  and top with toasted bread cubes and cheese then place under broiler until cheese is melted and bubbly. Serve.

Recipe Video

Vegetarian French Onion Soup

5 from 3 votes
Prep: 15 minutes
Cook: 1 hour 30 minutes
Total: 1 hour 45 minutes
Course: Soup
Cuisine: French
Calories: 311
Servings: 6 people
A vegetarian take on Julia Child's French Onion Soup recipe from her iconic book: Mastering the Art of French Cooking

Ingredients  

  • 3 tablespoons butter salted or unsalted butter
  • 1 1/2 pounds onions thinly sliced (I used yellow onion)
  • 6 ounces crusty bread 1/2-inch thick slices, crusts removed and cut into 1-inch squares
  • 2 teaspoons kosher salt
  • 1/4 teaspoon sugar (helps the onions to caramelize)
  • 3 tablespoons all-purpose flour
  • 1 teaspoon fresh thyme leaves from 4 large sprigs or 1/2 teaspoon dried thyme
  • 1 cup dry white wine
  • 8 cups mushroom broth or vegetable broth
  • 2 tablespoons Cognac
  • kosher salt and freshly ground black pepper to taste
  • 3 ounces finely grated Gruyère cheese

Instructions 

  • Melt butter in a large pot or Dutch oven over medium heat. Add onion and stir to coat. Reduce heat to low; cover and cook 15 minutes.
  • Meanwhile, make the toasted bread cubes (croutons): Preheat oven to 400°F. 
  • Line a baking sheet with parchment paper and spread bread cubes in a single layer. Bake until crisp and golden brown, 12 to 15 minutes. Remove from oven and set aside.
  • Uncover onions and stir in salt and sugar. Raise heat to medium-low; cook 40 to 50 minutes, stirring often until onions have caramelized to a deep golden brown.
  • Add flour; cook and stir 3 minutes to remove flour taste. Add thyme, wine, and mushroom broth to onion mixture and stir, scraping up any browned bits. Increase heat to medium-high and bring to simmer. Reduce heat and let simmer, stirring occasionally, 30 to 40 minutes to your desired taste and consistency. Remove from heat and stir in Cognac. Add salt and pepper to taste
  • Preheat broiler.
  • Ladle soup into 6 individual broiler-safe bowls. Top each bowl with 1/6 each of the toasted bread cubes and shredded cheese.  Arrange bowls on a baking sheet and place under broiler. Broil until cheese is melted and bubbly. Serve.

Notes

If you don’t want 6 servings of this soup at once, make the full recipe of onion soup, but prepare just enough bread and cheese for the number of servings you want. Then reheat the leftover soup as needed, finishing with bread and cheese. The croutons will keep for at least a week in an airtight container at room temperature.

Nutrition

Calories: 311kcal | Carbohydrates: 35g | Protein: 9g | Fat: 11g | Saturated Fat: 6g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 3g | Trans Fat: 1g | Cholesterol: 31mg | Sodium: 2278mg | Potassium: 250mg | Fiber: 3g | Sugar: 9g | Vitamin A: 995IU | Vitamin C: 9mg | Calcium: 190mg | Iron: 2mg

Nutrition information is automatically calculated, so should only be used as an approximation.

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10 Comments

  1. Michele says:

    I just cooked this tonight. It was delicious. My vegetarian husband was craving French onion soup. I didn’t have ramekins so I improvised with making foil cups of croutons topped with cheese and broiled them placed the bundles over the soup in bowls. Thanks!

    1. Marissa Stevens says:

      What a fun way to serve this, Michele! So glad to hear that you and your husband enjoyed it.

  2. Valentina says:

    Marissa, this sounds absolutely incredible! I love the use of mushroom broth instead of veg — so deep and rich! And the touch of cognac is brilliant! 🙂 ~Valentina

    1. Marissa Stevens says:

      Thanks so much, Valentina!

  3. David @ Spiced says:

    5 stars
    What a fun idea to make this classic soup into a vegetarian version! I haven’t cooked much with mushroom broth, but I have seen it in the stores. Now I’m wondering if you can make your own – it shouldn’t be that hard, right!?

    1. Marissa Stevens says:

      I haven’t tried making my own, but I bet you’re right, David. I imagine that dried mushrooms would work well for creating a homemade version.

  4. Lori says:

    5 stars
    You’re my hero! I’ve been wanting a good vegetarian version of this for so long. Thank you!

    1. Marissa Stevens says:

      My pleasure, Lori! So glad you enjoyed this.

  5. Rachel Haus says:

    5 stars
    Just made this for the family. My husband, who lived for a year in Paris, pronounced it fabulous! Being vegetarian, I threw in a few extra tricks — I couldn’t find mushroom broth, but made a quick version by soaking dried mushrooms and using the liquid along with a vegan “beef” broth. I also added powered fennel, which adds a beefy flavor to soups and stews. Also, not having cognac, I threw in a little rum and red wine at the end. Wonderful!

    1. Marissa Stevens says:

      Thank you, Rachel!