This classic vegan French onion soup is deeply savory and flavorful, thanks to patiently caramelized onions. It has a brothy texture and is topped with vegan cheese toasts. The cheese can be homemade, which I give instructions for, or store-bought: the choice is yours! French onion soup is a recipe that requires some time, but the steps are actually very straightforward—and the results are oh-so-worthwhile.

I have always loved French onion soup.

One of my earliest memories of eating in a restaurant involves French onion soup.

I was with my mother and grandmothe. I forget which one of them had ordered the soup. But when it arrived to the table, my grandmother encouraged me to try it.

The salty, savory broth was enough to win me over. But it was the top layer of toasted bread and cheese, which had soaked up some of the broth beneath it, that won me over.

It has taken me quite some years to attempt a vegan French onion soup recipe of my own, but I finally have. And I’m so very glad that I did.

Like all French soup, this one will require some patience on your part, but I promise you won’t be sorry.

What is French onion soup?

French onion soup is a soup made of onions that have been caramelized and simmered in some sort of broth.

French onion soup is served gratinée, or topped with toasted bread or croutons and cheese.

The history of a humble soup

When I started to think about tackling French onion soup at home, I wondered whether it’s actually French, or rather an American recipe that’s inspired by characteristics of French cuisine.

As it turns out, French onion soup does in fact hail from France.

Onion soups have been enjoyed for centuries. However, it wasn’t until the 19th century that the version familiar to us now took shape.

The famous Parisian food market, Les Halles, as well as some of the restaurants around it, began serving French onion soup with gratinée bread and cheese on top.

According to writer Emily Monaco, French onion soup is not only a long-cherished hangover cure, but a historically egalitarian dish, eaten by Parisians of all classes. For most of history, soups have been accessible to many, thanks to their generally inexpensive ingredients.

French onion soup began to make its way around the world later in the 19th century. It was dubbed “French onion soup” in Great Britain in the 1880s, and it first appeared in an American restaurant in 1861.

Variations of French onion soup

Most French onion soup recipes call for caramelizing onions with some type of fat, then simmering them in liquid.

That liquid can be broth alone, or it can be broth that’s thickened a bit with flour. Occasionally, I’ve seen variations that call for milk or cream.

As for the topping, it can be made of big, chunky croutons, which are topped with grated cheese, or small cheese toasts.

The bread can be sliced from a boule or loaf, or it can be small slices of baguette.

The cheese, meanwhile, is usually Gruyère. However, I’ve seen recipes that call for Emmental, Parmesan, Asiago, or even Mozzarella.

This vegan French onion soup will give you the option of using a homemade, melty, cashew-based cheese or commercial vegan cheese shreds.

I’ve tried both versions, and they’re enjoyable in different ways. The homemade cheese gets irresistibly browned in the broiler, while the commercial version melts and stretches more easily.

As I was experimenting with this soup, I tried adding various things to the brothy base: carrots, celery, herbs.

In the end, I liked—and am sharing—a purist’s version. This classic vegan French onion soup is all about the onions, and that’s how I think it should be.

Caramelizing onions 101

At the end of the day, making a good pot of French onion soup comes down to one single, all-important process: caramelizing onions.

Truthfully, there’s so much written about how to properly caramelize onions that I feel almost silly offering my own information.

However, the amount of instruction available on this topic can be almost overwhelming, so maybe there’s value in extracting some basic points.

First: what does it mean to caramelize onions?

Caramelizing onions is the process of cooking onions over low(ish) heat for a long(ish) period of time.

The long, slow cooking process will allow the natural sugars in the onions to oxidize, or brown, taking on sweet, nutty flavors.

That’s caramelization. It’s the same caramelization that would happen if you were to make candy or caramel sauce with a sugar and water solution; in this case, it’s happening to the natural sugars in a vegetable.

How is caramelization different from sautéing, or roasting?

If you’ve made oven-roasted onions or sautéed onions over high heat, then you’ve probably seen that the onions will almost always start to brown.

How is that browning different from caramelization?

The difference comes down to two factors: time and temperature.

Caramelized onions cook at a lower temperature for a longer period of time than do sautéed onions. As a result, their sugars oxidize more completely, and they take on a deeper, sweet flavor.

Sautéed or roasted onions will brown, but they generally retain more savory notes and sharpness than do caramelized onions.

How long does it take to caramelize onions?

Generally, caramelizing onions takes 40-60 minutes. A small batch of onions will likely take less time, whereas a large batch will take longer.

Each time I’ve made this vegan French onion soup, it’s taken me about 50 minutes to fully caramelize the onions.

Caramelized onions tips and tricks

Caramelizing onions is a culinary topic that inspires strong opinions. I don’t pretend to have definitive or expert guidance, but there are a few techniques that I find very helpful and worth sharing.

Tip 1: Don’t raise your heat too high

When you’ve been stirring a pot of onions every few minutes for over half an hour, it’s mighty tempting to crank the heat in order to cook the onions faster.

Try to resist this urge. Yes, raising the heat will create more browning, but this isn’t quite the same as caramelization.

If you don’t allow that low-and-slow effect to happen, then you may end up with burnt onions, rather than caramelized onions.

Tip 2: Choose a cooking vessel with a wide bottom

Since the caramelized onions in this recipe turn into vegan French onion soup, you’ll want to cook them in a large, heavy-bottomed pot. I recommend a pot with a reasonably wide diameter, rather than a tall and narrow stockpot.

If you make caramelized onions on their own, then I recommend a large, deep skillet over a pot.

Why? Surface area. More surface area gives more of the onions a chance to come into contact with heat and cook slowly.

A more narrow pot can work, but it will require more stirring, and possibly more time.

Tip 3: Stir every 10 (or so) minutes

There’s a delicate balance between stirring too often and too little while you’re caramelizing onions.

If you stir too much, you won’t actually give the onions a chance to spend time in contact with their heat source, browning beautifully.

If you stir too little, then the onions can start to burn and turn bitter, rather than caramelize and turn sweet savory.

I think stirring every 8-10 minutes is the right amount. It’s enough stirring to keep moving the onions around and making sure that they all come into contact with the bottom of the pot. Yet it’s also enough resting time to help them all brown.

Can I caramelize onions in a non-stick pan?

When I moved apartments some time ago, I invested in the Caraway Non-Toxic Ceramic Nonstick Cookware Set. It was a great investment; I’ve been totally happy with my cookware since then. (You can find my full review here.)

As I was preparing to make this vegan French onion soup, I wondered whether the nonstick surface would be an issue. I’ve read many times over that nonstick cookware isn’t ideal for caramelizing onions.

My verdict? Nonstick cookware may not be optimal for caramelizing onions, but it can certainly handle the job.

I think the major difference is the amount of time needed to kickstart caramelization. It takes a bit longer to begin seeing real browning throughout the onions in nonstick, as compared with stainless steel or cast iron.

Ultimately, however, time and heat will work their magic, and the onions will caramelize. Have faith, and trust the process!

Do I need to add sugar to the onions?

Many guides to caramelizing onions direct the home cook to add sugar.

It’s true that sugar will help to move the caramelization process along. And it also adds some additional, caramel-like flavor to the onions.

When I make caramelized onions that aren’t intended to be turned into soup, I do add a little brown sugar (I also stir some balsamic vinegar in at the end).

For this soup, however, I don’t think that sugar enhances or contributes to the flavor. So there’s no need to add it.

What type of onions should I use?

In a pinch, you can use pretty much any type of onion. I’ve caramelized red, white, yellow, and sweet onions.

Sweet onions are my favorite for caramelizing, but I’ve used white onions many times, too. You can even use shallots—though you’d need a whole lot of shallots for this particular recipe!

Olive oil vs. vegan butter

There are some French onion soup recipes that call for the use of butter as a fat source, and others that call for oil.

When I developed this vegan French onion soup, I wondered whether I ought to use vegan butter or olive oil.

I tried both options, and I was surprised to find that olive oil worked every bit as well as vegan butter. Since vegan butter is more of a specialty product, I chose to list olive oil in the ingredient list.

However, you can use vegan butter if it’s your preference.

A word about broth

Traditional onion soup can be made with beef, chicken, or vegetable broth. You can make this recipe with a plant-based version of any of those types of broth.

Beef broth is the most traditional onion soup base, and I prefer a vegan beef-style broth myself. My favorite these days is the Born Simple Beef-Style Broth Concentrate, but Better than Bouillon is a good option as well.

You’ll need a fair amount of broth for the recipe—a whole eight cups.

The other thing to say about the broth here is that it shouldn’t be ice cold. Use broth that is room temperature or prepared with hot water. If you’re reconstituting a bouillon cube or powder, you’ll be using warm liquid, anyway.

How to make vegan French onion soup

As you begin making this recipe, just remember: patience. This is recipe isn’t hard, but it is a commitment. If you know that upfront, you can relax, settle into the process, and enjoy it.

Step 1: Slice your onions

Be prepared to take some time doing this, since the soup calls for about 3 pounds of onion!

To slice the onions for your vegan French onion soup, you’ll trim them and cut them in half lengthwise.

Then, use a slicer or chef’s knife to trim and thinly slice the onions. The slices should be about 3/16-1/4 inch / 4-6mm wide from root to stem.

Step 2: Caramelize your onions

This step is the big step.

You’ll begin by heating olive oil in a large, heavy-bottomed pot over medium high heat. Add the onions and salt.

At first, the onions will crowd the pot and fill it almost completely. As you stir them and coat them with oil, they’ll soften and reduce in size.

Cover the pot and begin the caramelization process, stirring the onions every 10 minutes. You can expect the caramelization step to take 40-60 minutes in total.

Step 3: Add garlic and white wine

Once the onions have browned to perfection, it’s time to season the onions and start to build the foundation of a soup.

Garlic and white wine—I recommend something dry—are part of that process. You can omit the wine altogether if you like, but I don’t recommend skipping the garlic.

Step 4: Add a little flour

I think the soup takes on extra richness when you add just a small amount of flour to thicken it at this point.

Sprinkle two tablespoons of all-purpose flour (regular or gluten-free) lightly over the onions. Cook, stirring constantly, for a few minutes, or until the onions have thickened and the flour has cooked a little.

Add a cup of broth very slowly, stirring as you go. Then, add the remaining broth, two bay leaves, and a splash of vinegar to the pot.

Step 5: Simmer

Turn the heat to high and bring the soup to a simmer, then turn the heat back to low. Simmer the soup, covered, for 30 minutes. Remove the bay leaves, taste the soup, and adjust the salt and pepper as you like.

Step 6: Make cheese toast

Now it’s time to prepare those tasty gratinée cheese toasts for the soup.

I offer two cheese options for the toast. One is a nice batch of my melty vegan cashew mozzarella cheese.

This cheese is creamy and has a slightly stretchy consistency. It’s very versatile; I use it for topping baked lasagna or shells, for my vegan broccoli melts, and for pizza.

Once you make a batch of the cheese, you’ll spread it—be sure to do this while the cheese is hot—onto pre-toasted slices of bread.

I use the broiler to toast the bread. One or two minutes per side is enough; it will toast more when it returns to the broiler with cheese on top.

The bread you use can be from a round boule, or you can do triangles of sandwich-shaped bread. You can also use crosswise slices of baguette.

If you don’t have time to make your own vegan cheese, no problem. There are so many good, commercial vegan cheese shreds these days, which melt and stretch nicely.

My favorite are the mozzarella shreds from Good Planet Foods, but many other brands make this style of cheese.

In addition, you don’t have to use store-bought cheese shreds; you could also use slices of vegan mozzarella, American cheese, or Gouda-style cheese.

After you top your bread with cheese, you’ll transfer it to the broiler once again and give it 3-4 minutes, or until the cheese is toasty and melted.

Step 7: Top the soup with the cheese toast

At this point, you’ll divide the soup into bowls or ramekins and top each portion with the cheese toast.

If you use a smaller container, like a ramekin, the toast will cover all of the soup. If you use a bigger bowl, the cheese toast will probably be partially submerged into the soup.

At this point, it’s time to dip, dunk, and enjoy!

Make-ahead options

The vegan French onion soup is a wonderful option for meal prep and make-ahead cooking.

The soup itself can be stored in an airtight container in the fridge for up to 1 week and frozen for up to 6 weeks. 

If you make the melty cashew mozzarella cheese, it can be stored in an airtight container in the fridge for up to four days.

It will thicken in the fridge, but that’s OK; just spread it directly onto your bread when you’re ready to make toasts.

What to serve with vegan French onion soup

This soup is so hearty and warming that it could be a light meal unto itself.

However, I’m always a fan of serving any main dish with a vegetable side dish or two. Here are a few, salads mostly, that I think would pair nicely with the vegan French onion soup:

• Quick steamed green beans with Dijon vinaigrette
• My favorite butter lettuce side salad
• Crispy broccoli Caesar salad
• Perfect winter chopped salad
• Winter panzanella salad
• Brussels sprout kale salad
• Cauliflower pomegranate kale salad
• Radicchio Brussels sprout salad

No matter how you choose to serve this time-honored, comforting soup, I hope you’ll love it.

December is right around the corner, which means that we’re officially diving into the heart of winter.

My hope is that you’ll find many moments of coziness curled up with a bowl of this vegan French onion soup—and a crusty, broth-soaked slice of cheese toast.

Enjoy!

xo