Vegetarian French Onion Soup Recipe — Savory Caramelized Onion Soup

Vegetarian French onion soup is a meat-free take on the French classic. Comforting and rich, the soup features sweet, slowly cooked onions in a savory broth, finished with a slice of crusty bread and a blanket of melted cheese — pure comfort in a bowl.

What’s in vegetarian French onion soup?

This simple, flavorful soup relies on a few key ingredients:

Butter (or olive oil to make it vegan)
Yellow onions (thinly sliced)
Sugar (helps with caramelization)
Flour (optional, for slight thickening)
White wine (optional)
Vegetable bouillon cube or good vegetable stock
Bay leaf
A slice of sturdy bread per bowl
Gruyère or another easily melting cheese
Salt and freshly ground black pepper

How to make French onion soup

Step 1: Heat the butter in a medium saucepan over medium heat (use olive oil for a vegan version).
Step 2: Add the sliced onions with a pinch of salt and cook for about 5 minutes to start softening them.
Step 3: Continue cooking the onions until they begin to brown and caramelize, stirring occasionally.
Step 4: Stir in the sugar and flour, cooking for another minute to combine and slightly thicken.
Step 5: Pour in the white wine (if using) and simmer for 3–5 minutes to reduce the alcohol and concentrate flavor.
Step 6: Add the vegetable stock, a 1/2 teaspoon of ground black pepper, and the bay leaf. Simmer gently for about 30 minutes.
Step 7: Preheat the oven to 400°F with the broiler setting ready.
Step 8: Divide the soup between two ovenproof bowls.
Step 9: Place a slice of bread on top of each bowl and heap about 1/2 cup (or to taste) of grated cheese over the bread.
Step 10: Broil in the oven just until the cheese is melted, bubbly and lightly browned, about 3–5 minutes. Serve hot.

Tips to make this vegetarian onion soup

Use a high-quality melting cheese like Gruyère for authentic flavor. Cheddar, mozzarella, provolone or smoked cheeses can be tasty alternatives.
Take your time caramelizing the onions — deep color and concentrated sweetness are what give this soup its signature taste.
If you prefer a gluten-free version, omit the flour and skip the bread topping, or use a gluten-free slice.
For a vegan version, swap butter for olive oil, and top with a vegan cheese or omit cheese entirely. Ensure the wine and stock are vegan-friendly if needed.

What kind of cheese is best?

Gruyère is the traditional choice because it melts well and adds a nutty, savory note. Feel free to experiment with cheeses you enjoy — cheddar, provolone or mozzarella all work.

Which onions are best?

You can use different onions depending on the flavor you want:

Yellow onions: Classic choice with balanced sweetness and a touch of bitterness.
Red onions: Deeper, slightly more assertive flavor.
Sweet onions: Milder and very sweet, for a softer, rounder soup.

Ways to vary the recipe

Add cooked chicken for a heartier, non-vegetarian version.
Top with crunchy croutons for texture instead of or in addition to a bread slice.
Use the soup as a flavorful base in casseroles, meatloaf mixes, or as a topping for burgers.

Is this French onion soup vegetarian?

Yes — this version uses vegetable stock and no meat products, so it is fully vegetarian.

Can it be made vegan?

Yes. Replace butter with olive oil, use vegan stock and wine, and top with vegan cheese or omit the cheese entirely.

Can you make the soup without wine?

Absolutely. Simply omit the wine and add a little extra stock; the soup will still be delicious.

Is it gluten free?

To make a gluten-free version, skip the flour used for thickening and use gluten-free bread or omit the bread topping altogether.

What to serve with French onion soup

The soup is satisfying on its own, but it pairs wonderfully with a fresh baguette or slices of grainy bread and a simple green salad.