Easy Vegetarian French Onion Soup (Stovetop or Crockpot)

This vegetarian French onion soup (vegan optional) is rich, decadent, super savory, and comforting – a perfect lunch or dinner for the chilly winter months! With a combination of slowly caramelized onions, a splash of white wine, and a melted cheesy garlic bread topping, this easy French onion soup is the ultimate comfort food made on the stovetop or in a crockpot!

If you like the sound of slowly caramelized onions combined within a rich and intense veggie broth, increased depth of flavor with a splash of wine (optional), then topped with a garlic and cheesy bread topping, I don’t blame you. Luckily, that’s precisely what this vegetarian French onion soup is!

Rich and Comforting Easy Vegetarian French Onion Soup

Slowly caramelizing the onions adds impressive depth to the ingredient, bringing out their natural sweetness and making for a thick, rich vegetable-based soup packed with depth and the perfect “stick to your ribs” winter soup. Unlike the original, which uses beef stock, this vegetarian French onion soup is 100% vegetarian and can even be made vegan with a few simple ingredient swaps.

Within this post, I’ll take you through how to make this rich soup as a stovetop or crockpot French onion soup, as well as top tips, notes, and what to serve with a French onion soup. In fact, I’ll give you a free bonus top tip right now: any recipe that calls for less than at least 40 minutes of caramelizing the onions, click away. Likewise, anyone trying to convince you to ditch the super cheesy bread topping is not to be trusted!

It may take a while, but the majority of the process is fairly hands-off. Plus, it’s a great excuse to make a double batch and store one in the freezer for later! Not to mention that the end results are so flavor-packed that not only will you not even notice the missing beef broth, but this veggie French onion soup tastes restaurant-quality!

Looking for more easy comfort food classics? You might enjoy this mixed veggie lasagna, Lebanese butter bean stew, Greek stuffed vegetables, bolognese scalloped potato roll, etc.

Vegetarian French Onion Soup Ingredients

The French Onion Soup

• Onions: and lots of them for a truly delicious veggie French onion soup. I like to use yellow onions (keep reading for more info on the best onions for French onion soup).
• Garlic: adjust the amount to personal taste.
• Flour: use all-purpose flour – this is needed to thicken the soup. Read the FAQs for substitutes.
• Olive oil: use olive oil or another neutral cooking oil. Butter/ghee would also work for even sweeter results.
• Thyme: I used dried thyme, as it’s all I had. However, you could use double the amount of fresh thyme (using a couple of thyme sprigs) instead.
• Vegetable stock: I use homemade vegetable stock. Use reduced-sodium stock if preferred and adjust the amount of salt in the recipe accordingly.
• White wine: use dry white wine (make sure it’s vegan if necessary). Brandy, sherry, or vermouth would also work.
• Sugar: this is technically optional depending on what onions you use and how sweet you prefer the soup. I use just a pinch of sugar (or a sugar-free alternative like erythritol) to enhance the natural sweetness of the veggie French onion soup.

The Cheesy Bread Topping

• Bread: we use a classic bread and cheese topping for this veggie French onion soup. In terms of bread, use gluten-free bread if necessary. Baguette slices work particularly well size-wise though any crusty artisan bread (not soft bread) works well to hold up to the liquidy veggie French onion soup without falling apart. Or you can use croutons.
• Cheese: Gruyere is the traditional cheese for French onion soup. However, Swiss cheese, Gouda, Emmental, Jarlsberg, or even a combination of mozzarella and cheddar/vegetarian parmesan would work. DON’T use pre-shredded cheese as it won’t melt properly!

What are the Best Onions for French Onion Soup?

The type of onion you use in this vegetarian French onion soup will affect the overall flavor of the soup. Your main options include:

• Yellow onion: wonderfully mild and sweet once caramelized with only a hint of bitterness, perfect for building depth of flavor to soups and stews.
• White onion: similar to yellow onions, though milder in flavor. This is an excellent alternative to yellow onions.
• Red onion: will yield a more robust but still sweet flavor. I also find red onions slightly more bitter when making this vegetarian French onion soup.
• Sweet onions: not an option I’ve tried before. However, the mild, sweet flavor of these onions makes them great for caramelizing but may result in a soup that’s sweeter than you’d like unless mixed with other onions, too (and omit any extra sugar). I recommend using 1 sweet onion mixed with one of the other varieties.

You could also experiment with using shallots, which are fairly sweet but with a rich flavor too.

Feel free to experiment with each and a blend of various ones to find your perfect combination! In my opinion, the best onions for French onion soup are yellow onions, which yield the most balanced and not OVERLY sweet flavor.

Optional Add-Ins & Recipe Variations

• Dark soy sauce: this can help to mimic some of the richness in the traditionally used beef broth. However, it’s also packed with sodium, so it’s best when using low-sodium veg stock.
• Bay leaves: add 1-2 bay leaves for extra depth of flavor.
• Sage: instead of thyme, sage is a popular addition to English French soup.
• Black pepper: adjust amount to personal taste.
• French onion soup without wine: the simplest option is just to use additional vegetable stock. However, I prefer to add 2-3 tablespoons of wine vinegar (which doesn’t actually contain alcohol), balsamic vinegar/cider vinegar for extra depth of flavor. You could also use grape juice, but remember that it will be sweet, so omit the added sugar in the recipe.
• Mushroom broth: for extra umami flavor, you can use a bit of mushroom broth in place of the vegetable broth.
• Vegan French onion soup: use vegan butter or olive oil and vegan cheese (experiment to find your desired taste and meltability).
• Chives: finely chopped chives make for a great fresh garnish to the vegetarian French onion soup.
• Add spice: a pinch of red pepper flakes would add a subtle layer of spice.
• Classic French onion soup: feel free to use rich beef stock (or chicken stock as an alternative) if you eat animal products.
• Make it gluten–free: use gluten-free all-purpose flour and bread for a simple gluten-free French onion soup.

How to Make Vegetarian French Onion Soup?

Step 1: Prepare the Onion

First, peel and thinly slice the onions. I do this by slicing off the root and stem ends of the onion, chopping it in half (from top to bottom), then placing the onion halves cut-side down and slicing (make cuts about ¼-inch apart).

You can save the onion peel/scraps to make homemade vegetable stock.

Then, heat the olive oil in a large deep-bottomed soup pot/Dutch oven over medium-high heat. Once hot, add the onions and cook, stirring often, for around 10 minutes until they’re beginning to brown.

If you notice pieces burning rather than just browning, reduce the heat slightly. Make sure to stir well to lift up browned bits from the bottom of your pot each time you stir. You can lightly deglaze the pan with a splash of your stock or wine as needed at the end of the process, too (before adding flour).

Meanwhile, chop one of the garlic cloves (if you use more than 2 cloves, make sure to keep one to one side) and add it to the onions along with the sugar and dried thyme.

Stir well, reduce the heat to medium, and cook for 30 minutes. Stir infrequently to begin (every 4-5 minutes) and more so towards the end (every 1-2 minutes), as they’re more likely to burn once reduced/caramelized.

Adjust the time if needed until you achieve soft and slightly sweet onions with a rich golden brown color. Feel free to move on to the next step earlier if you like the taste when the onions are slightly less caramelized. For more tips, check How To Caramelize Onions!

Step 2: Add the Liquids

Add the flour to the pan and stir well to combine, allowing it to cook for 2 minutes. Then add the wine (use it to deglaze the pan and scrape up any browned bits from the bottom of the pan) and veggie/beef stock, stirring well, and bring the mixture to a rolling boil.

Skim and foam from the surface of the soup, then lower the heat to a gentle simmer, cover with a lid, and allow it to cook for a further 40-45 minutes.

Step 3: Prepare the Cheesy Bread Topping

First, preheat the grill.

Then, toast the bread slices under the broiler (usually 5-8 minutes total), rubbing each piece with the remainder of the garlic.

Pour the soup into oven-safe bowls/ramekins (wide enough for your bread pieces), filling them ¾ way. Then place a piece of the toast in each bowl and top with freshly grated cheese until you can’t see the soup below (don’t be stingy!).

If you don’t own oven-safe bowls/containers, then whip up a batch of cheesy garlic bread to serve with the vegetarian French onion soup instead (i.e. spread the toasted bread on a baking sheet, top with cheese, and broil BEFORE adding to the soup). That way, they’ll spend less time in contact with the soup, too, meaning less soggy bread.

Broil for several minutes until the cheese has melted and is beginning to bubble. It’s best to broil them around 6-inches/15cm away from the heat source).

Serve piping hot!

What to serve with French onion soup?

Like most soups, there are several ways you can enjoy this vegetarian French onion soup, whether alone or with a side, including:

• A simple leafy green salad like Caesar salad or this simple kale salad.
• A grilled cheese (use vegan cheese if preferred) or sandwich (i.e., with a sweet element like apples or pears).
• With simple veggie sides like sauteed green beans, broccoli, sauteed spinach, sauteed mushrooms, etc.

You can also use leftovers to help make dishes like French onion soup burgers or topped hotdogs!

How to Make Ahead and Store?

Make ahead: you can prepare the entire soup (minus the cheesy bread topping) up to 2 days in advance, then reheat when needed and add the topping (the flavor will develop in the fridge and taste even better!). You could also leave the onions to caramelize in a slow cooker overnight (check FAQs for method), then continue with the soup on the stovetop the next day.

Store: allow the soup to cool (minus the bread/cheese topping) and then transfer to an airtight container in the refrigerator for 3-4 days.

Freeze: transfer the cooled soup (minus the bread/cheese topping) to an airtight container or Ziplock bags (portioned, with headspace) and freeze for up to 3 months. Allow the frozen French onion soup to thaw in the refrigerator before reheating or speed up the process by placing the bag/container in a bowl of hot water.

Reheat: you can use a microwave or the stovetop to reheat the soup gently until heated through. Add an extra splash of broth or water if needed.

FAQs

Recipe Tips and Notes

• Adjust the amount of sugar: I like to add “just” enough for a very subtle sweetness. However, feel free to adjust the amount to personal taste.
• Don’t over-brown the onions: or you may end up with an overly bitter soup. Instead, feel free to taste the onions while caramelizing to find your desired level (anything past a light caramel could work).
• Don’t over broil the cheese: if it’s still primarily golden and just beginning to bubble, then it will still be gooey and melty. Make it more browned/crispy, and you’ll miss out on the gooeyness.
• Cut the onions uniformly: that way, they’ll caramelize evenly too. Using a mandoline (carefully) to slice the onions can help for consistent results.
• Don’t rush the soup: possibly the most crucial tip of all. This vegetarian French onion soup is all about the rich flavor from the slowly caramelized onions, so don’t try any shortcuts!

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• Roasted garlic, mushroom, and potato soup
• Lebanese lentil soup
• Cream of mushroom soup
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• Japanese Ramen noodle soup
• Quick and Easy Chicken and Rice Soup (in 30 Minutes)
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• Simple Lebanese Lentil Soup (Vegan Lentil Soup)
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• Vegetarian Minestrone Soup (Vegetable Tomato Pasta Soup | 3 Methods)

If you try this vegetarian French onion soup recipe, I’d love to hear your thoughts/questions below. Also, I’d appreciate a recipe card rating below, and tag me in your recipe recreations on Instagram @Alphafoodie!