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This vegetarian French onion soup recipe is made with perfectly caramelized onions and a few other simple ingredients. It’s one of the coziest cool-weather meals around!

Why You’ll Love This French Onion Soup Recipe

Vegetarian. Traditional French onion soup is made with beef broth. We’re using vegetable broth though, which makes this recipe vegetarian friendly.
Ultra cozy. There’s nothing quite like the pleasure of sticking your spoon through a layer of melty cheese and crusty bread to get to the deeply flavorful soup underneath. When you get a bite of soup, bread, and cheese all in one mouthful it’s pure magic.
Easy to make. French onion soup is not hard to make. It does require a bit of time though, so that you can caramelize the onions before making the soup.
Great leftovers. French onion soup reheats well! Just store the soup, bread & cheese separately.

Caramelized onions in a dutch oven with a wooden spoon

How to Caramelize Onions

Caramelizing onions is a low and slow method of cooking onions until they take on a light golden color. It adds incredible flavor! In my opinion, it is not difficult to do, but it does require patience and attention to detail. The caramelization process takes 45 minutes to 1 hour and you need to stir the onions frequently. This means you need to have time to kill in the kitchen and you can’t rush the process.

Here are some tips for perfectly caramelized onions every time:

Use oil and butter. My recipe calls for both oil and butter and the reason is simple – butter can burn too easily. When you add some olive oil to the mix that is much less likely to happen.
Don’t slice the onions too thin. You don’t want to use thick slices of onion because those will be difficult to caramelize. On the flip side, you don’t want your onions to be too thin because then they will fall apart. Aim for about 1/8th inch thick.
Use a large pot. If you use a small pot then the onions will be in a thick clump and will steam instead of caramelizing. A large dutch oven is ideal, but a big soup pot also works. I like to use the same pot I’m going to make the soup in.
Low and slow. Don’t crank the heat up in the expectation of making the process go faster. If your heat is too high your onions will burn, so stick to medium-low the entire time.

How do you know when your onions have finished caramelizing? They will be a rich golden brown color and very soft but not mushy.

Ingredients for french onion soup on a table

Ingredient Notes

For a full list of ingredients and specific amounts, please be sure to scroll down to the recipe card. These are just my notes on some of the ingredients we’ll be using.

Yellow onions. Vidalia onions are the best kind of onion to use for French onion soup. You can get away with white onions if you must. Definitely don’t use red onions.
Unsalted butter. Salt is added separately while making this recipe, so if you use salted butter there’s a good chance your finished product will be too salty.
Vegetable broth. Traditionally French onion soup is made with beef broth. You can use vegetable, beef, or even chicken broth. I use vegetable broth to make this recipe vegetarian friendly.
Swiss cheese. Most French onion soup recipes use shredded Gruyere cheese, but I prefer to use slices of Swiss cheese. I find that shredded cheese often falls off the bowls and burns onto the baking sheet as well as the sides of each bowl. A couple of slices of swiss cheese give you an even layer of melty cheese across the top of your soup. Emmental, Jarlsberg, or a combination of mozzarella and provolone also work well.
What kind of bread to use? I recommend a French baguette. You need to use crusty bread about the width of the bowl. The crustiness is key – soft bread will fall apart when placed into the soup.

Is This a Vegetarian French Onion Soup?

Yes, because I use vegetable broth instead of beef broth this recipe is vegetarian. 🙂 It’s not vegan though because, well, butter and cheese.

How to Make French Onion Soup

Are you ready to make this easy french onion soup recipe? Here’s how to do it:

Mixing caramelized onions with flour in a dutch oven — Caramelized onions with wine and flour.

Making french onion soup in a dutch oven — Caramelized onions with wine and flour.

Caramelize the onions. Melt the butter in a large heavy pot over medium heat. Add oil, the sliced onions and salt. Stir frequently and cook for about 5 minutes, giving the onions time to soften. Reduce the heat to medium-low and continue cooking, stirring often, until the onions are a light golden color. This will take about 60 minutes.
Add wine and flour. When the onions are finished, add the wine and bring the mixture to a simmer. Add the flour and mix well, stirring constantly for a couple of minutes until the mixture thickens. Scrape the bottom of your pot to get all the flavorful bits that have stuck there.
Add broth, vinegar and pepper. Stir the broth into the pot. Add the sherry vinegar. Taste and season with black pepper and salt.

Cook the soup. Simmer over medium-low heat for 30 minutes, stirring often.
Toast the bread. Slice your french bread and lightly toast the pieces in your toaster oven.
Add the bread and cheese. Ladle the soup into oven-safe single-serving bowls and place the bowls on a baking sheet. Top each bowl with a slice of toasted bread and then a slice or two of cheese.
Broil. Place the bowls in the oven and turn on the broiler. Broil for 1-2 minutes, until the cheese melts. Keep an eye on it so that the cheese doesn’t burn!
Serve. Remove the bowls from the oven and with oven mitts carefully move the hot bowls to serving plates. Dig in!

What Kind of Bowl to Use

It is extremely important that you use oven-safe bowls to finish this soup. Amazon has a wide selection of oven-safe single-serving bowls with handles, which makes it easier to move the bowls when they are hot.

A spoon with a mouthful of french onion soup

What Goes With French Onion Soup?

French onion soup can be served on its own, but I often serve it with crispy grilled cheese sandwiches on the side. You could also serve it with more slices of crusty bread or even popovers, which can be used to sop up any last bits of soup in your bowl.

If you don’t want to juggle finishing the soup with making grilled cheeses on the stovetop, these baked grilled cheese sandwiches are a lifesaver.

How to Store and Reheat Extras

Fridge: Ladle cooled soup into airtight containers and store it in the fridge for up to 5 days.
Freezer: Spoon the soup into freezer-safe, airtight containers and store it in the freezer for up to 3 months. Make sure you leave at least 1 inch of space at the top of your container so that the soup has room to expand as it freezes. Thaw overnight in the fridge when you’re ready.
Reheat: Add the desired amount into a small pot and reheat over a medium-low flame until warmed through. You can also reheat single servings in microwave-safe bowls. Once hot, toast up some bread and finish the soup as described in the recipe below.

Vegetarian French Onion Soup