This famous French onion soup is a perfect one-dish meal. It culminates in a rich onions that will warm you up on cold winter nights. It is also vegetarian, light and easy to make. After you’ve tried this version, you will never be able to enjoy another one.
1/2 cup unsalted butter
2 pounds yellow onions (about 6 medium), thinly sliced lengthwise
8 to 10 sprigs fresh thyme
1 teaspoon kosher salt, plus more for seasoning
1 teaspoon freshly ground black pepper, plus more as necessary
1 tablespoon flour
1 cup dry white wine
4 cups mushroom stock
2 cups vegetable stock
1 1/2 cups cubed ciabatta bread
3 cups grated Gruyere cheese
1. In a large pot, melt the butter over low heat. Add the sliced onions, thyme, salt, and pepper and saute, stirring occasionally until the onions become a deep golden brown, about 30 minutes.
2. Add the flour and cook for 1 to 2 minutes. Add the white wine and scrape up the bottom of the pan, increasing the heat to a boil for 2 to 3 minutes. Add the mushroom stock and the vegetable stock, and allow the soup to simmer for an additional 30 minutes. Season the soup with salt and pepper, to taste.
3. Preheat the oven to broil. Arrange the ciabatta cubes on a baking sheet and toast until crispy.
4. Remove the thyme sprigs and pour the soup into 4 to 6 oven-safe bowls. Top with the toasted ciabatta cubes and a generous amount of grated Gruyere.
5. Place the bowls under the broiler for 3 to 5 minutes, or until the cheese is melted.