This easy Vegetarian French Onion Soup recipe is comforting and satisfying for a chilly day. Lentils contribute a boost of protein and added nutrition, while melted gruyere toasties round out the whole dish.
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You know that feeling when you really nail a dish? When all the flavors just come together perfectly, and you know it’s going to be a crowd-pleaser?
That’s how I feel about this fantastic Vegetarian French Onion Soup! I’m really not trying to toot my own horn, but I just can’t help but gush about this recipe. And, believe me, the deliciousness of this dish has more to do with the ingredients than anything else!
In one simple bowl, you’ll taste caramelized yellow and sweet onions, green lentils cooked in vegetable broth and dry white wine, and hints of fresh thyme and balsamic vinegar.
OH, and did I mention the irresistible toasties that you place on top of each bowl, with perfectly melted gruyere cheese? Yeah, they’re the bomb.
Are you drooling as much as I am?
PS – While you’re here, check out the Celeriac and Apple Soup, Apple Ginger Kabocha Squash Soup, Creamy Broccoli and Potato Soup with Peas, and Butternut Squash and Pear Soup.
What kind of onions do you use for French onion soup?
For this recipe, I recommend a mix of yellow and sweet onions, but you can use any variety! Sweet onions are the sweetest variety, white onions have a sharper taste, yellow onions have an equally sweet and pungent flavor, and red onions are the least sweet and can be slightly bitter.
You need about 3 pounds of onions for this recipe, so ~6-8 small or medium onions or 4-5 larger onions.
How to Make Vegetarian French Onion Soup
French onion soup takes a while to cook, because the onions need to cook down before you add the broth and other ingredients, but it involves very little “active” cooking.
So, don’t be afraid to make this Vegetarian French Onion Soup on a weeknight! Just make sure you watch it on the stove while you catch up on housework, reading, emails, etc.
For those of you who aren’t familiar with making French onion soup, it’s usually made with beef broth. However, I substituted vegetable broth in this version, so it’s veg-friendly.
I also added lentils to this recipe to increase the nutrition and protein content. They help make this soup a more filling main dish.
Here’s a peek at how to make this recipe (more details in the recipe card):
- Slice the onions in half-moons. Sautee them in butter and olive oil over medium-low heat. Let them cook down for 40-45 minutes, or until they are caramelized and have shrunk in size (see photo above).
- Add the garlic and flour, and stir. Cook for a few more minutes. Add the broth, white wine, thyme, balsamic, and dried lentils.
- Bring to a boil, cover, then reduce heat to a low simmer. Cook for 20-25 minutes.
- Ladle the soup into oven-safe bowls (preferably French onion soup bowls if you have them). Add 1-2 slices of a baguette on top. Cover with shredded gruyere cheese. Put under the broiler for a few minutes.
Craving more onion recipes? Check out my Whole Roasted Onions and Caramelized Onion White Bean Dip!
- To slice onions for vegetarian French onion soup, start by slicing off the ends, cutting the onion in half lengthwise, and peeling off the skin. Then use a sharp knife to slice each half into “half moon” pieces.
- The best kind of bread to use on top of French onion soup is a French baguette. I prefer sourdough. Slice it into thin pieces and toast for 1-2 minutes on a baking sheet under the broiler before putting on top of the soup bowls.
- What can I use instead of gruyere? Sub cheddar cheese or gouda.
- To make vegetarian French onion soup without alcohol, skip the wine and add 2 more teaspoons of balsamic vinegar instead.
- If you have them, use a wooden spoon and an enameled cast iron Dutch oven (like a Lodge or Le Creuset) or a stainless steel pot, so that you will be able to de-glaze all of the caramelized onion bits off the bottom of the pot. But these tools are certainly not necessary to make this recipe.
- You can caramelize onions ahead of time, then freeze or refrigerate them to make this soup at a later time.
- Store in an airtight container in the fridge for 4-5 days or freezer for up to 3 months (thaw frozen soup overnight in the fridge before reheating). Reheat on the stove or in the microwave. If you have the time, add fresh gruyere toasties on top before eating.
I’d love to hear how you like this recipe! Rate/review using the stars on the recipe card or in the comments, and follow the Veg World on YouTube, Instagram, Facebook, and Pinterest. Looking for something totally different? Browse the recipe library.
Vegetarian French Onion Soup with Lentils
- enameled cast iron pot (like a Dutch oven) or stainless steel pot
- wooden spoon
- 4 large yellow and sweet onions - ~3 pounds; can sub any variety
- 2 tablespoon butter
- 2 tablespoon olive oil
- 2 cloves garlic - pressed or minced
- ½ teaspoon sea salt
- 2 tablespoon all purpose flour
- ½ cup dry white wine - I used Pinot Grigio
- 6 cups vegetable broth
- 1 tablespoon balsamic vinegar
- 1 tablespoon fresh thyme - more to taste
- 1 cup green lentils - dried (not cooked), rinsed, and sorted
- 10 thin slices French baguette - for serving
- 1 cup gruyere - freshly shredded
- Slice the bottoms off the onions and remove their skins, then cut in half from top to bottom. Slice each onion half into thin, half-moon slices.
- Heat the butter and olive oil in a large pot over medium heat. Add the onions and cook for 5 minutes. Stir, and reduce heat to medium-low. Let the onions cook, stirring occasionally, until they shrink down and get brown in color, about 40-45 minutes. If you want to cook them for a longer time for a stronger caramelized taste, you can.
- Add the salt, flour, and garlic to the onions once they are caramelized to your liking. Stir and cook for a few more minutes.
- Pour the white wine into the pot and use your spoon to scrape off any of the bits of caramelized onion stuck to the bottom. Add the vegetable broth, balsamic, thyme, and dried lentils to the pot. Increase heat and bring to a boil. Cover, then reduce heat to low and let the soup simmer for 20-25 minutes, or until the lentils are tender.
- While the soup is cooking, slice the baguette and shred the cheese. If desired, you can toast the baguette slices by placing them on a baking sheet under the broiler for a couple of minutes.
- Ladle the soup into oven-safe bowls, top with 1-2 slices of bread, and sprinkle the shredded Gruyere evenly over the bowls. Transfer the bowls to the oven, by placing them directly on the center rack or on a baking sheet, and turn on the broiler to high. Cook for 1-2 minutes or until the cheese is melted. Carefully remove from oven and enjoy!
- You can use any type of French baguette, but sourdough tastes especially good.
- No gruyere? Sub cheddar or gouda.
- For even more of a savory flavor, add a tablespoon of soy sauce or tamari at the same time as the balsamic.
- To make without alcohol, skip the wine and add 2 more teaspoon of balsamic vinegar.
- To make vegan, use all olive oil instead of butter and oil and nix the cheese.
- Onions can be caramelized ahead of time and frozen or refrigerated to be used later to make this soup.
- Store in an airtight container in the fridge for 4-5 days or freezer for up to 3 months (thaw frozen soup overnight in the fridge). Reheat on the stove or in the microwave.
Hope you enjoy this cozy meal as much as I do!
Wonderful soup, thank you!
Lizzie Streit, MS, RDN
I’m glad to hear you enjoyed it! Thanks for leaving a review!
Hey Lizzie! This looks lovely!! Do you have any recommendations as a substitution for those who can have lentils?
Lizzie Streit, MS, RDN
Hi! Thank you, I’m glad you think so! Good question. Although I have not tried it personally, I think that dried white or navy beans might be a good substitution for the lentils. But since most dried beans would take longer to cook than the lentils in the soup, I’d recommend soaking the beans beforehand if you can. You can soak them in a bowl of water in the fridge for a few hours or overnight. Or, you can probably get away without soaking them at all…you would just need to cook the soup for a while longer. Let me know how it turns out if you try!