Classic Vegetarian French Onion Soup Recipe

When you crave cozy, warming comfort food, this easy, hearty Vegetarian French Onion Soup is a perfect choice. Slow-cooked sweet onions create a rich base, and the addition of dried porcini mushrooms and a splash of soy sauce brings deep, savory umami—even without any beef broth.

This version delivers classic French onion flavor in a meat-free format. It’s straightforward to prepare: thinly slice the onions, caramelize them, add a simple roux and deglaze with vermouth, then simmer with vegetable stock, porcini, soy sauce, and thyme. Finish each serving with a toasted baguette slice and a blanket of melty cheese under the broiler for that iconic gratinéed top.

Vegetarian French Onion Soup – Ingredient Highlights

Use yellow onions for the best balance: they caramelize well and avoid the extra sweetness that red or Vidalia onions can add. If you don’t have Dry Vermouth, a dry white wine or a touch of white wine vinegar can be used instead.

Because this recipe omits beef broth, dried porcini mushrooms and soy sauce supply the savory depth and complexity that traditionally comes from meat-based stock. Together they create a full, satisfying flavor so you won’t miss beef at all.

For topping, Gouda melts beautifully and adds a slightly sweet, nutty note, but Gruyère, Swiss, mozzarella, or even Brie will work. Choose any melty cheese you enjoy.

French Onion Soup (No Beef Broth) Tips & Tricks

How to Make French Onion Soup without Beef Broth

Slicing the onions is the most time-consuming step. Cut each onion into quarters around the core, lay the quarters flat, and slice into roughly 1/4-inch strips so they soften and cook evenly. Wear contact lenses or goggles if you’re sensitive to the fumes.

Start by melting butter in a large pot or Dutch oven over medium-high heat. Add the sliced onions and cook, stirring frequently, until they are tender and translucent, about 10–15 minutes. Add the flour, salt, and pepper and stir to coat the onions and form a light roux. Pour in the Dry Vermouth and stir until the flour has fully integrated and there are no lumps.

Stir in vegetable broth, diced rehydrated porcini mushrooms, soy sauce, and fresh thyme leaves. Bring the pot to a boil, then reduce the heat, cover, and simmer for 20–30 minutes to allow the flavors to meld. Taste and adjust seasoning before serving.

How to Serve French Onion Soup Topped with Bread and Cheese

Preheat the oven to 400°F (200°C). Slice a French baguette into 1-inch-thick pieces, brush both sides with extra-virgin olive oil, and arrange them on a baking sheet. Toast on the bottom rack until crispy and golden, about 8–10 minutes.

Ladle the soup into oven-safe crocks, float a toasted baguette slice on top of each bowl, and pile on a generous amount of your chosen cheese. Place the filled crocks on a baking sheet and move them to the top rack of the oven. Bake for about 5 minutes, until the cheese is melted and bubbling. Garnish with fresh thyme and serve immediately with extra toasted bread for dipping.

How I Store and Reheat French Onion Soup

Let any leftover soup cool to room temperature, then transfer it to an airtight container. Store in the refrigerator for 3–5 days. Reheat gently on the stovetop over medium heat until warmed through, or microwave in a covered, microwave-safe bowl, checking and stirring after each minute until hot.

Store any extra toasted baguette separately in an airtight bag and refresh in a 400°F oven for about 5 minutes, or use a toaster. For the classic experience, add fresh toasted bread and cheese when reheating individual portions.

Recipe: Easy Vegetarian French Onion Soup

Equipment

• Dutch oven or large heavy-bottomed pot
• Oven-safe soup crocks or mini cocottes (optional)

Ingredients

• 5 medium yellow onions, peeled, cored, and thinly sliced
• 2 tablespoons unsalted butter
• 1/4 cup all-purpose flour
• 1/2 teaspoon salt
• 1/2 teaspoon black pepper
• 1/2 cup Dry Vermouth (or dry white wine / a splash of white wine vinegar)
• 4 cups vegetable broth
• 1/4 cup dried porcini mushrooms, diced (rehydrate in a little warm water if desired)
• 2 tablespoons soy sauce
• 1 tablespoon fresh thyme leaves (+ extra for garnish)
• 1/2 French baguette, sliced into 1-inch pieces
• 2 tablespoons extra virgin olive oil
• 4 ounces Gouda or other melty cheese, sliced or shredded

Instructions

1. Peel, core, and slice the onions into 1/4-inch strips. Dice the dried porcini mushrooms if needed and remove thyme leaves from their stems.
2. Melt the butter in a large pot or Dutch oven over medium-high heat. Add the onions and cook, stirring frequently, for 10–15 minutes until tender and translucent.
3. Add the flour, salt, and pepper, stirring to coat the onions and form a light roux.
4. Pour in the Dry Vermouth and stir until the flour is fully incorporated and the mixture is smooth.
5. Add the vegetable broth, diced porcini mushrooms, soy sauce, and fresh thyme. Bring to a boil, then reduce heat, cover, and simmer for 20–30 minutes, stirring occasionally.
6. While the soup simmers, preheat the oven to 400°F (200°C). Brush baguette slices with olive oil and toast on a baking sheet until golden and crisp, about 8–10 minutes.
7. Ladle the hot soup into oven-safe bowls, top each with a toasted baguette slice, and cover with a generous amount of cheese.
8. Place bowls on a baking sheet and broil or bake on the top rack of the oven for about 5 minutes, until the cheese is melted and bubbling. Garnish with thyme and serve hot.

Pro Tips

• Toast the bread before topping the soup to prevent it from becoming too soggy.
• If you don’t have individual oven-safe crocks, place the bread and cheese directly on the soup in the Dutch oven and finish under the broiler until bubbly.
• Adjust soy sauce to taste for more or less umami, and rehydrate porcini in warm water for an even deeper mushroom flavor.

This vegetarian take on French Onion Soup is rich, comforting, and easy to make. The combination of caramelized onions, porcini, and soy sauce creates a satisfying depth of flavor without any meat—perfect for colder evenings or as a special family meal.