Meatless Monday Challenge

Hearty Vegetarian French Onion Soup

on May 4, 2021
last updated August 14, 2023
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This flavor-packed Vegetarian French Onion Soup is filling, comforting, and downright delicious while being completely meatless!
croquette with vegetarian french onion soup with two more servings in the background

Looking for a full-of-flavor, meatless comfort food dinner option? This Vegetarian French Onion Soup is for you!

With a delicious and hearty onion and mushroom broth, this soup is only made better by the toasted bread and cheese on top! Add a little fresh thyme for an herbal finish and there you have it! The perfect vegetarian soup.

As an environmental scientist, I can’t get enough One-Pot meals! Using fewer dishes means less clean up which means–you guessed it! Less wasting water!

Green tip: Speaking of water usage and clean up, if you have a dishwasher, use it! Comparing dishwashing to handwashing, using an efficient dishwasher uses up to 1/6th the amount of water to get your dishes equally as clean.

Vegetarian French Onion Soup Tips and Tricks

Prep Your Ingredients First

Start by collecting your ingredients to stay organized. Dice your onions, mince your garlic, and remove your thyme leaves from the stems. Here’s what you’ll need:

all the ingredients you need to make vegetarian french onion soup

Tested Substitutions

Vegetable stock can be substituted for mushroom stock in a pinch, but you may have to add more seasonings. Vegetable broth doesn’t have the same, earthy, umami flavor, so just taste as you go!

You can absolutely substitute plant-based butter to fry up your onions and make your roux.

I love using Gouda cheese on top because it melts so beautifully and has notes of sweetness and nuttiness! But you can really use any melty cheese—Gruyere, Mozzarella, Swiss, even Brie!

pulling cheesy bread apart in front of bowl of soup

Start with a Roux

Add your diced onions to a large pot or Dutch Oven and sauté them in the butter until they are translucent and fragrant. This should take about 8 minutes over medium heat.

Once your onions are ready, add your flour and stir until your onions are coated. This process is forming your roux, which is the base to the hearty consistency of your soup.

The soup should come together perfectly from here!

Green tip: It is estimated that 50% of food waste happens at home. The average shelf life of all-purpose flour is about 8 months, but freezing it can extend its life by another year and a half! Just store it in an airtight container and stick it in the freezer.

Toast Your Bread

After preheating your oven and slicing your bread, drizzle the pieces of bread with olive oil and toast it in the oven for 10 minutes.

This will avoid your French bread from getting soggy while it soaks up the delicious soup!

Transfer Your Soup to Little Croquettes

Once your soup is ready for its final bake, transfer them to little oven-safe croquettes. Float a slice of toasted bread on top, add your sliced or grated cheese, and garnish with some fresh thyme.

In just 5 minutes at 400 degrees Fahrenheit, your cheese will be melty, bread toasty and saturated with delicious soup, and your kitchen will smell like a dream!

Should You Have Leftovers

If you have leftover soup, allow it to cool, transfer it to an airtight container, and store it in the refrigerator for up to 3 days.

You can reheat it over the stove in a pot on medium heat or in the microwave. Put it in a microwave-safe dish with an aerated lid and microwave on high for about 3 minutes. Stir and assess temperature. If needed, heat for another minute or two.

If you have leftover bread, wrap it and store it separately, and reheat it in the oven at 400°F for about 5 minutes or in the toaster.

individual serving of french onion soup with spoon next to it

Why You Should Make This Vegetarian Soup

  • It’s bursting with flavor. The mushroom stock and onions lend so much flavor to the broth.
  • It’s classic comfort food. Warm soup finished with bread and cheese—doesn’t get cozier than that!
  • It’s easy to clean up! Throw it all into one pot to cook!

If you’re loving this Vegetarian French Onion Soup and want other hearty meatless meals, check out this Vegetarian Broccoli Cheddar Soup and Vegetarian Ramen.

croquette with vegetarian french onion soup with two more servings in the background

Vegetarian French Onion Soup

5 from 2 votes
Marley Goldin
Print Save Rate
This flavor-packed Vegetarian French Onion Soup is filling, comforting, and downright delicious while being completely meatless!
Prep Time 30 minutes
Cook Time 40 minutes
Total Time 1 hour 10 minutes
Servings 4 servings



  • 3 large onions
  • 3 tablespoons unsalted butter
  • 3 tablespoons all-purpose flour
  • ½ cup dry Vermouth
  • 4 cloves garlic, minced
  • 4 cups mushroom stock
  • 1 bay leaf
  • 2 sprigs fresh thyme leaves, chopped + more for garnish
  • ¼ teaspoon onion powder
  • ¼ teaspoon salt
  • ¼ teaspoon black pepper
  • 1 whole French baguette
  • 1 tablespoon extra virgin olive oil
  • 4 ounces Gouda cheese, sliced or shredded
Shop Ingredients on Jupiter


  • Add your diced onions and butter to a large pot or Dutch Oven, and sauté over medium heat until onions are translucent and fragrant—about 8 minutes.
  • Add the flour and stir until onions are coated.
  • Add Vermouth and stir, until flour is mixed in.
  • Add garlic and simmer for 5 minutes, stirring occasionally.
  • Add the mushroom stock, bay leaf, thyme, salt, pepper, and onion powder and stir. Cover and simmer for 20 minutes.
  • Preheat oven to 400°F and slice French baguette, to make pieces about 1 & 1/2 – 2 inches thick.
  • Drizzle olive oil on bread, and toast on a baking sheet in the oven for ten minutes.
  • Remove soup from heat and ladle into oven-safe individual soup bowls. Top each serving with sliced bread and gouda, and garnish with more thyme.
  • Place individual servings on a baking sheet, and bake at 400°F for 5 minutes, until cheese is melted and bubbly.
  • Serve hot with extra toasted bread to dip in. Enjoy!

Pro Tips

  • Toast your bread before adding it to your soup to avoid it getting soggy!
  • If you don’t have individual croquettes, you can put the bread and cheese on top of the soup in your Dutch oven, and stick it in the oven for 400°F to melt the cheese.
  • It’s hard to beat a good bowl of soup! Check out my most delicious selection of hearty soup recipes!

Share This Recipe

Course Dinner, Lunch
Cuisine French
Diet Vegetarian
Keyword French Onion Soup, Vegetarian French Onion Soup
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