Classic Caramelized Onion Soup with Gruyère

1. Soften the Onions

Begin by melting the butter in a heavy Dutch oven over medium heat. Once the butter has melted, add the thinly sliced onions and 0.5 teaspoons of kosher salt. Stir the onions to coat them thoroughly with the butter, then cover the Dutch oven and let the onions soften for about 5 minutes.

2. Caramelize the Onions

After the onions have softened, remove the lid and continue cooking the onions, stirring occasionally. This is the most crucial step as you're aiming to caramelize the onions, which can take between 45 to 60 minutes. Patience is key here; let the onions cook until they turn a deep golden brown. If the onions are browning too quickly, reduce the heat slightly to avoid burning.

3. Warm the Beef Stock

While your onions are caramelizing, warm the beef stock in a separate saucepan over low heat. This ensures that the broth is ready to be added to the soup without cooling down the cooking process.

4. Deglaze and Thicken

Once the onions are beautifully caramelized, add the dry white wine and dry sherry to the pot. Bring the mixture to a boil, which helps to deglaze the pan, lifting all those flavorful browned bits from the bottom. Next, stir in the all-purpose flour and cook for about 1 to 2 minutes to thicken the mixture slightly, creating a smooth base for your soup.

5. Combine Ingredients

Gradually add the warm beef stock to the onion mixture, stirring constantly. Add another 0.25 teaspoons of kosher salt and 0.5 teaspoons of black pepper. Bring the soup to a boil and then let it simmer uncovered for about 10 minutes, allowing the flavors to meld together perfectly.

6. Prepare Bread and Cheese

While the soup is simmering, preheat your broiler. Arrange individual ovenproof casseroles on a baking sheet, and ladle the hot soup into each one. Place a slice of French bread on top of each serving of soup, ensuring it covers the surface.

7. Broil the Cheese

Generously sprinkle the grated Gruyère cheese over the bread. Place the casseroles under the broiler for 1 to 2 minutes, keeping a close eye on them. You want the cheese to melt and turn a beautiful golden brown without burning.

8. Serve

Once the cheese is melted and bubbly, carefully remove the casseroles from the oven and serve the soup immediately. Enjoy the rich, comforting flavors of this classic caramelized onion soup with the perfect touch of melted Gruyère on top.