Hearty Vegetarian French Onion Soup

When you want cozy and warming comfort food, it doesn’t get any better than this Hearty Vegetarian French Onion Soup.

Loaded with flavor from the tender onions, the addition of porcini mushrooms and soy sauce adds tons of umami, for a soup that has depth in every bite.

Even with no beef broth, I’m confident that this will be one of the best soups you ever make (along with my viral Pastina soup with blended vegetables, because that one is ALWAYS a crowd pleaser!).

Plus, once your onions are sliced, it’s really easy to make! You basically dump everything into one big pot to make the soup and then finishing it off in the oven in an individual serving with toasted baguette and melty cheese. Need I say more? Let’s get into it!

As a proponent of a sustainable lifestyle, I can’t get enough One-Pot meals! Using fewer dishes means less cleanup and of course 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 Ingredients

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Here’s everything you need:

• Yellow onions.
• Unsalted butter.
• All-purpose flour.
• Salt & pepper.
• Dry Vermouth. Or white wine, or even white wine vinegar.
• Vegetable broth.
• Dried porcini mushrooms.
• Soy sauce. While this may seem out of place for a French Onion soup recipe, removing the beef broth to make it vegetarian means we have to add something a little extra to get that depth of flavor and umami. Between the porcini mushrooms and soy sauce, you will not miss the beef broth at all!
• Fresh thyme.
• French baguette.
• Cheese. 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!

How to Make French Onion Soup without Beef Broth

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Prep Your Onions

Slicing the onions is by far the most difficult part of making this soup. I definitely make sure I wear my contact lenses when I’m making this recipe to shield my eyes haha!

You want your onions sliced pretty thin, so they cook down quicker and get nice and tender. They do shrink a bit when they cook, so I usually chop them into ¼-inch thick slices.

Make sure to discard your onion peels and cores (or compost them or save them to make your own vegetable broth!).

I find the easiest approach to prepping your onions is by cutting the onion in 4 pieces around the core, so you can then lay the quarters flat and slice them.

Make Your Vegetarian French Onion Soup

Add the butter to a large pot, Dutch Oven, or Cocotte over medium-high heat and let it melt and start to get hot. Add your sliced onions and cook over medium-high heat, tossing frequently, until the onions are tender (10-15 minutes).

Then, add the flour, salt, and pepper and stir to coat to form a roux. Add the Dry Vermouth next and stir again to mix in the flour.

Now, add the broth, diced porcini mushrooms, soy sauce, and fresh thyme leaves. Bring to a boil, then cover, turn down the heat to low, and simmer for about 20-25 minutes to allow the flavor to develop.

Slice and Toast the Baguette

Preheat the oven to 400°F and slice your baguette into roughly 1-inch-thick pieces. Line them up on a baking sheet and brush both sides with olive oil.

Toast them in the oven on the bottom rack for about 8-10 minutes, until crispy and golden brown. I like to toast extra bread to serve alongside the soup for dipping, but you can just toast as much as you want.

If you are toasting less than half a loaf, it may take less than 8 minutes, check on it after 5 to make sure it doesn’t burn.

Assemble Your Soup to Serve

Add individual servings to oven-safe soup crocks and place them on the baking sheet for easy transfer into the oven. Float the toasted baguette on the soup and layer a generous amount of cheese on top.

Place the crocks on the baking sheet back in the oven at 400°F, on the top rack this time for about 5 minutes until the cheese gets all melty.

How to Properly Store and Reheat French Onion Soup

If you have leftover soup, allow it to cool, transfer it to an airtight container, and store it in the refrigerator for 3-5 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.

Always finish your leftover soup off with some extra bread and cheese to get that classic French Onion touch every time!

Why You Should Make This Vegetarian Version of French Onion Soup

• It’s bursting with flavor. Aside from the super flavorful onions, the addition of porcini mushrooms and soy sauce brings tons of umami and depth of flavor to the soup.
• 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!