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Vegetarian French Onion Soup

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

French onion soup is one of my favorite cold-weather foods. It’s hearty, cozy and makes your home smell incredible.

Plus, 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.

French onion soup is not hard to make, but it does require patience. This is because the onions need to be caramelized before they are used to make the soup and this process takes about an hour. I usually make this soup on the weekends when I’m baking something in the kitchen and can be around to stir the onions every 10-15 minutes. French onion soup reheats well though, so you could make this on a Sunday for supper on Monday.

A blue ramekin with french onion soup

Why is it Called French Onion Soup?

Onion soups have been popular for centuries and date back to the Roman era. It was often a preferred soup for the poor because onions were plentiful and easy to grow. The modern version, however, originated in 18th-century France and is traditionally made with beef broth and caramelized onions. In this vegetarian french onion soup recipe we’ll use vegetable broth instead of beef broth.

There are many variations of French onion soup however one thing is consistent: the onions are almost always cooked slowly until they are caramelized. This deepens their flavor and adds a subtle sweetness to them. The soup is then usually served with toasted bread on top. When the bread is topped with cheese and then broiled in the oven it is called gratinéed French onion soup.

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 in a pinch if you really must. Definitely don’t use red onions.
  • Unsalted butter. Use unsalted butter so that you can control the amount of sodium in your food. 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 will use shredded Gruyere cheese, but I prefer to use slices of Swiss cheese. Why? Because I find that shredded cheese often falls off the bowls and burns onto the baking sheet as well as the sides of each bowl. I also don’t want to fuss with thinly slicing a block of Gruyere. A couple of slices of swiss cheese give you an even layer of melty cheese across the top of your soup. You can use Gruyere cheese if you prefer though. 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:

  • Caramelize the onions. Melt the butter in a large heavy pot over medium heat. Add oil and the sliced onions and 1 teaspoon of kosher 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 have finished caramelizing, 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. Pour the broth into the pot, stirring as you add it to make sure it is well incorporated. Stir in the sherry vinegar. Taste and season with black pepper. You can add more salt if needed at this point.
French onion soup in a dutch oven
  • Cook the soup. Simmer over medium-low heat for 30 minutes, stirring often.
  • Toast the bread. While the soup is simmering, slice your french bread and lightly toast the pieces in your toaster oven.
  • Add the bread and cheese. Ladle the soup into oven-proof single-serving bowls and place the bowls on a baking sheet, which makes it easier to get them in and out of the oven. Top each bowl with a slice of toasted french bread and then a slice or two of swiss cheese. You can also use shredded Gruyere 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 (affiliate link) 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: Let your soup cool to room temperature, then ladle it into airtight containers and store it in the fridge for up to 5 days.
  • Freezer: If you want to freeze the soup, ladle it 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 to eat some.
  • Reheat: When you’re ready to reheat, simply ladle 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.
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French Onion Soup

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

  • Author: Rustic Family Recipes
  • Prep Time: 15 minutes
  • Cook Time: 1 hour 30 minutes
  • Total Time: 1 hour 45 minutes
  • Yield: 4-5 servings
  • Category: Soup
  • Method: Stovetop
  • Cuisine: French

Ingredients

  • 3 tablespoons unsalted butter
  • 1 tablespoon olive oil
  • 5 large yellow Vidalia onions, peeled and thinly sliced
  • 1 teaspoon kosher salt, plus more to taste
  • 1 cup dry white wine
  • 1 tablespoon all-purpose flour
  • 67 cups vegetable broth, according to your preference
  • 1 tablespoon sherry vinegar
  • ½ teaspoon black pepper, more to taste
  • French bread cut into slices
  • 46 slices swiss cheese

Instructions

Caramelize the onions. Melt the butter in a large heavy pot over medium heat. Add oil and the sliced onions and 1 teaspoon of kosher 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 have finished caramelizing, 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. Pour the broth into the pot, stirring as you add it to make sure it is well incorporated. Stir in the sherry vinegar. Taste and season with black pepper. You can add more salt if needed at this point.

Cook the soup. Simmer over medium-low heat for 30 minutes, stirring often.

Toast the bread. While the soup is simmering, slice your french bread and lightly toast the pieces in your toaster oven.

Add the bread and cheese. Ladle the soup into oven-proof single-serving bowls and place the bowls on a baking sheet, which makes it easier to get them in and out of the oven. Top each bowl with a slice of toasted french bread and then a slice or two of swiss cheese. You can also use shredded Gruyere 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!

Keywords: french onion soup recipe, easy french onion soup, vegetarian french onion soup

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