Vegetarian French Onion Soup Recipe — Rich, Savory & Simple

This vegetarian French onion soup tastes remarkably like the classic version thanks to one umami-rich swap: mushroom broth. The result is deep, savory, and comforting—everything you want in a bowl of French onion soup, made without meat (and easily vegan).

Umami—the Japanese term for the fifth taste after sweet, sour, bitter, and salty—gives this soup its rich, rounded flavor. When paired with slowly caramelized onions, white wine, a splash of cognac, crusty toasted bread, and melted Gruyère (or Comté), the mushroom broth provides the savory backbone that makes this vegetarian version taste like the original.

Ingredients You Need to Make Vegetarian French Onion Soup

• Butter: high-fat European-style butter is ideal, but any salted or unsalted butter will work.
• Onions: yellow, sweet, or red onions (or a mix) thinly sliced.
• Bread: crusty French or peasant bread (crusts removed) or cubed baguette, toasted until crisp.
• Flour: all-purpose flour to thicken slightly.
• Thyme: fresh thyme leaves or dried thyme.
• Wine: a dry white wine you’d enjoy drinking; the flavor concentrates as it cooks.
• Broth: mushroom broth is the key; vegetable broth can be used in a pinch.
• Cognac: or brandy for finishing (optional).
• Sugar: a small amount to help the onions caramelize.
• Cheese: Gruyère or Comté (or another melting Swiss-style cheese).
• Kosher Salt and Freshly Ground Black Pepper to taste.

The Magic Ingredient

Mushroom broth brings a meaty, umami-packed depth that vegetable broth often lacks. When I compared versions made with plain vegetable broth and mushroom broth, the mushroom-based soup more closely matched the richness and complexity of the traditional beef-based classic. If you want the closest vegetarian approximation, mushroom broth is the ingredient to choose.

Why this tastes just like the traditional version.

The technique and remaining ingredients mirror a classic French onion soup: long, slow caramelization of butter-coated onions, deglazing with white wine, simmering with flavorful broth and thyme, finishing with a splash of cognac, and topping with toasted bread and bubbling cheese under the broiler. The only meaningful swap is mushroom broth for beef stock—everything else keeps the familiar structure and flavors intact.

The soup does take time on the stove, but it’s mostly hands-off while it simmers in a Dutch oven. Caramelized onions are the heart of the dish; take your time and let them reach a deep golden-brown color for the best flavor.

FAQ

More Delicious Vegetarian Soup Recipes

• Tomato Bisque
• Vegan Butternut Squash Soup with Ginger
• Vegan Corn Chowder
• Delicata Squash Soup (vegan)
• Vegetable Soupe au Pistou
• Winter Squash Soup with Gruyère

How to Make Vegetarian French Onion Soup

Start by melting butter in a large pot or Dutch oven over medium heat. Add the sliced onions and stir to coat, then reduce the heat to low and cover. Cook the onions for about 15 minutes to soften.

While the onions begin to cook, prepare the toasted bread cubes on a baking sheet in a 400°F oven until crisp and golden. Set them aside.

Uncover the onions, add salt and a pinch of sugar, raise the heat to medium-low, and cook, stirring frequently, until they are deeply caramelized and golden brown.

Stir in the flour and cook for a few minutes to remove the raw flour taste. Add the thyme, white wine, and mushroom broth, scraping up any browned bits from the bottom of the pot. Bring the mixture to a simmer, then reduce the heat and let it simmer gently for 30–40 minutes to develop flavor. Remove from heat and stir in Cognac if using, then adjust salt and pepper to taste.

Ladle the hot soup into broiler-safe bowls, top each with toasted bread cubes and a generous amount of grated Gruyère or Comté, then place the bowls on a baking sheet and broil until the cheese is melted and bubbly. Serve immediately.

Vegetarian French Onion Soup

5 from 3 votes

By: Marissa Stevens

Prep: 15 mins

Cook: 1 hr 30 mins

Total: 1 hr 45 mins

Course: Soup

Cuisine: French

Calories: 311

Servings: 6 people

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A vegetarian adaptation of the classic French onion soup inspired by Julia Child’s method in Mastering the Art of French Cooking.

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Ingredients  

• 3 tablespoons butter salted or unsalted
• 1 1/2 pounds onions thinly sliced
• 6 ounces crusty bread 1/2-inch slices, crusts removed, cut into 1-inch squares
• 2 teaspoons kosher salt
• 1/4 teaspoon sugar (helps the onions caramelize)
• 3 tablespoons all-purpose flour
• 1 teaspoon fresh thyme leaves from 4 large sprigs (or 1/2 teaspoon dried)
• 1 cup dry white wine
• 8 cups mushroom broth or vegetable broth
• 2 tablespoons Cognac
• kosher salt and freshly ground black pepper to taste
• 3 ounces finely grated Gruyère cheese

Instructions 

• Melt butter in a large pot or Dutch oven over medium heat. Add onions and stir to coat. Reduce heat to low, cover, and cook 15 minutes.
• Meanwhile, make toasted bread cubes: preheat oven to 400 °F (204 °C). Spread bread cubes on a parchment-lined baking sheet and bake until crisp and golden, about 12–15 minutes. Set aside.
• Uncover the onions, stir in salt and sugar, raise heat to medium-low, and cook 40–50 minutes, stirring often, until onions are deeply caramelized.
• Add flour and cook, stirring, for 3 minutes. Add thyme, wine, and mushroom broth, scraping up browned bits. Bring to a simmer, then reduce heat and simmer 30–40 minutes. Remove from heat, stir in Cognac if using, and season with salt and pepper.
• Preheat the broiler.
• Ladle soup into 6 broiler-safe bowls. Top each with toasted bread cubes and shredded cheese. Arrange bowls on a baking sheet and broil until the cheese melts and bubbles. Serve hot.

Notes

If you don’t need six finished bowls at once, make the full pot of soup and prepare bread and cheese only for the number of servings you want. Reheat the remaining soup later and finish with bread and cheese when serving. Croutons will keep for about a week in an airtight container.

Nutrition

Calories: 311kcal

Nutrition information is an approximation.

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