The Best Vegetarian French Onion Soup Recipe

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This recipe is hearty, flavorful, & savory - without the meat! Baby bella mushrooms make this the Best Vegetarian French Onion Soup around.
A bowl of vegetarian french onion soup, baguette, and mushrooms.

French onion soup is perfect for a cold winter day, or anytime you’re looking for a warm, homey meal. Nothing beats a piping hot crock of soup covered in Gruyere cheese coming to your table at a restaurant. This is our homemade version – made vegetarian!

This dish has a very deep, rich, and savory flavor, traditionally made from a combination of beef broth and red wine. It’s absolutely delicious, but as vegetarians, we try to avoid all meat products, so the traditional french onion soup doesn’t work.

There are other vegetarian french onion soup recipes, but we found that they never quite produce the same meaty and hearty flavor from the beef broth. So, we decided to experiment and come up with our own recipe.

It turns out the secret ingredient to making an excellent vegetarian french onion soup is: baby bella mushrooms.

They are the perfect substitute for all the qualities that beef broth brings to the table. Baby bella mushrooms have a rich, savory flavor when cooked down, and take on a nice meaty texture. When combined with the sweet caramelized onions in this recipe, you’ll be in comfort food heaven.

A bowl of vegetarian french onion soup with a baguette.

Key Ingredients For This Vegetarian French Onion Soup

Caramelized Onions

Caramelized onions are dreamy in every which way – the sweet and rich flavor is something we wish we had in every meal. The only downfall is that they take forever to make. Thanks to the onions, plan for this recipe to take between and hour and an hour and a half.

If you like caramelized onions as much as we do, here’s an idea: make a huge batch and store them in the fridge for the rest of the week. Since they’re so time consuming, you might as well get the most out of it and enjoy them as long as possible.

Caramelized onions are absolutely excellent on sandwiches, toast, or grilled cheese. Apart from that, they basically go well on any warm dish that could use some extra flavor. Pasta, pizza, salad, grains, once again grilled cheese, quesadillas, omelettes – the possibilities are endless.

But back to the soup… cut up your onions and throw them in a large pan with butter. Mix or stir them occasionally. Sprinkle the brown sugar in once they start to turn brown. Other than that, remember that patience is key with caramelizing onions.

A bowl of vegetarian french onion soup with a baguette.

Baby Bella Mushrooms

Once you go baby bella, you never go back! They are so incredibly flavorful, rich, and meaty. Boring old white button mushrooms are a permanent thing of the past after your first recipe using baby bellas.

Wash them, dry them, and slice them. Start cooking them in your soup pot after you add the brown sugar to your onions. The olive oil helps keep the mushrooms from sticking to the bottom of the pot, otherwise they don’t need much else to get going.

These mushrooms hold an incredible amount of water. When heated, the water is released, along with some of the savory flavor they hold. To keep this flavor for your soup, keep the cover on your pot! You don’t want these yummy juices to evaporate.

Once the mushrooms have shrunk (you’ll be able to tell), add garlic, soy sauce, Worcestershire sauce, and paprika. Mhmmm, take in the sights and the smells.

After a few minutes, add the flour and mix thoroughly. The flour will thicken your mushroom mixture and provide a little extra volume.

It’s important to add the flour before any broth, so you can get any small clumps out. Nothing’s worse than finding chunks of flour in your finished product. The next step is to add the vegetable broth to the mushroom mixture, along with the thyme and pepper. Cover and let heat up until simmering, about 10 minutes.

A bowl of vegetarian french onion soup topped with a baguette and cheese.

The Finished Product: The Best Vegetarian French Onion Soup

At this point, you’ll have your soup pot with the mushrooms in it, and a frying pan with caramelized onions. Throw those onions in the soup, and let simmer for a few more minutes to truly mix the flavors.

Voila! You now have the best vegetarian french onion soup possible.

Now, toppings. Traditional french onion soup is served over toasted bread and topped with gruyere cheese. If you’ve never had gruyere, try not to judge by the taste and smell on its own. It’s a somewhat stinky cheese, but pairs perfectly with the richness of the soup.

The last time we made this, we had homemade baguettes from this recipe. Talk about easy and delicious! You can also buy crostinis from the store.

At restaurants, they finish french onion soup by covering the top in cheese and broiling it in the oven before serving. Unfortunately, we don’t own any appropriate dishes to do this. Instead, we toasted the baguettes with the cheese on top to melt them, and then put them in the soup.

There you have it! The best vegetarian french onion soup recipe you’ll find. Let us know in the comments if you try this recipe, and what you think!

Vegetarian French Onion Soup

A delicious vegetarian alternative to the classic soup, with the same hearty, rich flavor.
Prep Time 15 mins
Cook Time 1 hr 15 mins
Total Time 1 hr 30 mins
Course Appetizer, Main Course, Soup
Servings 4 people


Caramelized Onions

  • 3-4 large yellow onions sliced
  • 3 TBSP butter
  • 2 TBSP brown sugar


  • 16 oz baby bella mushrooms roughly sliced
  • 1 TBSP olive oil
  • 2 TBSP minced garlic
  • 2 TBSP soy sauce
  • 2 TBSP Worcestershire sauce
  • 1 tsp paprika
  • 3 TBSP flour
  • 6 cups vegetable broth
  • 1 tsp dried thyme
  • ½ tsp ground black pepper

Optional Toppings

  • shredded Gruyere cheese
  • toasted baguette slices


Caramelized Onions

  • Melt 3 tablespoons butter over medium-high heat in a large saute pan.
  • Add onions and cover for 30 minutes. Mix occasionally.
  • Once onions are limp and starting to brown, mix in brown sugar. Cover and cook until onions are caramelized to your liking, mixing occasionally.


  • After adding brown sugar to onions, heat olive oil in a large soup pot. Add sliced mushrooms and cover for 10 minutes. Mix occasionally.
  • Once mushrooms are reduced (shrunk in half with a simmering brown liquid on the bottom of the pot), add garlice, soy sauce, Worcestershire sauce, and paprika. Mix thoroughly and let simmer for 2-3 minutes.
  • While mixing, sprinkle in flour. Mix until no flour clumps are visible.
  • Add vegetable broth, thyme, and black pepper. Cover and heat until soup is simmering, 8-10 minutes.
  • Add caramalized onions to the soup, and mix. Cover and let simmer for another 5 minutes.


  • If wanted, toast baguette slices topped with Gruyere cheese until melted. Put in soup and enjoy!
Keyword autumn, caramelized onions, gruyere cheese, hearty, soup, vegetarian, warm, winter
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