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A spoon lifts a rich portion of classic french onion soup with perfectly melted, stringy Gruyère cheese over a toasted crouton and fresh thyme.
Daniel

Hearty French Onion Soup with Gruyère & Thyme

A classic bistro favorite, this rich and deeply flavorful French onion soup is made with slow-caramelized sweet onions, a savory beef and wine broth, and topped with a toasted baguette crouton and bubbly, melted Gruyère cheese.
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Prep Time 20 minutes
Cook Time 1 hour 30 minutes
Total Time 1 hour 50 minutes
Servings: 6 servings
Course: Appetizer, Main Course, Soup
Cuisine: French
Calories: 510
Ingredients Equipment Method Notes

Ingredients
  

For the Soup
  • 1/4 cup unsalted butter
  • 2 tbsp olive oil
  • 3 lbs yellow onions about 5-6 large onions, halved and thinly sliced pole-to-pole
  • 1 tsp granulated sugar helps with caramelization
  • 2 tsp kosher salt plus more to taste
  • 1/2 tsp freshly ground black pepper
  • 4 cloves garlic minced
  • 1/4 cup all-purpose flour
  • 1 cup dry white wine such as Sauvignon Blanc or Pinot Grigio
  • 8 cups beef broth high-quality, low-sodium
  • 1/4 cup brandy or cognac optional, but highly recommended
  • 3 sprigs fresh thyme
  • 1 bay leaf
For the Cheesy Croutons
  • 12 slices baguette cut 1/2-inch thick
  • 2 cups Gruyère cheese shredded
  • 1/2 cup Parmesan cheese shredded, optional

Equipment

  • Large Dutch oven or heavy-bottomed pot
  • Baking Sheet
  • 6 oven-safe soup bowls
  • Ladle

Method
 

Step 1: Caramelize the Onions
  1. In a large Dutch oven or heavy-bottomed pot, melt the butter with the olive oil over medium heat. Add the sliced onions and stir to coat. Cook, stirring occasionally, for 10 minutes until the onions begin to soften.
  2. Reduce the heat to medium-low, stir in the sugar, kosher salt, and black pepper. Continue to cook slowly for 60-70 minutes, stirring every 10-15 minutes, until the onions are deeply browned, sweet, and have a jam-like consistency. Be patient; this slow caramelization is the key to the soup's flavor. If the onions start to burn, reduce the heat and deglaze with a tablespoon of water.
  3. Add the minced garlic and cook for another 1-2 minutes until fragrant.
Step 2: Build the Soup
  1. Sprinkle the flour over the onions and stir constantly for 1 minute to cook out the raw flour taste.
  2. Increase the heat to medium-high and pour in the white wine to deglaze the pot. Scrape up any browned bits from the bottom of the pot. Let the wine bubble and reduce by about half, which should take 3-4 minutes.
  3. Gradually pour in the beef broth, stirring as you go. Add the brandy (if using), thyme sprigs, and bay leaf. Bring the soup to a gentle simmer, then reduce the heat to low, cover partially, and let it simmer for at least 30 minutes for the flavors to meld.
  4. Remove the thyme sprigs and bay leaf. Taste the soup and adjust seasoning with more salt and pepper as needed.
Step 3: Prepare Croutons and Broil
  1. While the soup is simmering, preheat your oven's broiler. Arrange the baguette slices on a baking sheet in a single layer. Broil for 1-2 minutes per side until golden brown and crisp. Watch carefully to prevent burning.
  2. Place 6 oven-safe bowls on a sturdy baking sheet. Ladle the hot soup into the bowls, filling them about three-quarters full.
  3. Float two toasted baguette slices on top of the soup in each bowl. Generously cover the baguette slices with the shredded Gruyère and Parmesan cheeses.
  4. Carefully place the baking sheet under the broiler. Broil for 3-5 minutes, or until the cheese is completely melted, bubbly, and beautifully browned in spots. Serve immediately, but caution your guests that the bowls will be extremely hot.

Notes

Patience is Key: Do not rush the onion caramelization. The deep, rich color and sweet flavor come from cooking them low and slow. It's the most important step!
Broth Quality: The flavor of your soup is heavily dependent on the quality of your beef broth. Use the best-quality, most flavorful broth you can find or make your own.
Make Ahead: The soup base (without the croutons) can be made up to 3 days in advance and stored in the refrigerator. Reheat gently on the stovetop before proceeding with the broiling step.
Cheese Variations: While Gruyère is classic, feel free to mix in other good melting cheeses like Comté, Emmental, or even a sharp white cheddar for a different flavor profile.