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French Onion Soup: The Cook’s Illustrated Way

The memory still warms me on chilly nights: Christmas Eve at my grandmother’s house, the air thick with the scent of woodsmoke and simmering onions. The entire family would crowd into the cozy kitchen, drawn by the promise of her French onion soup, a deeply savory elixir topped with a bubbling, golden crust of cheese. It wasn’t just the taste that lingered; it was the feeling of being surrounded by loved ones, sharing laughter and warmth over a truly exceptional bowl of soup. It was a tradition, a ritual, and a testament to the power of good food to bring people together.

Recipe Overview

Prep Time: 45 minutes
Cook Time: 4 hours 50 minutes (approximate, including passive roasting time)
Total Time: 5 hours 35 minutes (approximate)
Servings: 6
Yield: 6 bowls
Dietary Type: Not Gluten-Free

Ingredients

Soup:

3 tablespoons unsalted butter, cut into 3 pieces
6 large yellow onions, halved and cut pole to pole into 1/4-inch-thick slices (about 4 pounds)
Salt
2 cups water, plus extra for deglazing
1 tablespoon balsamic vinegar
4 cups low sodium chicken broth (such as Swanson Certified Organic Free Range)
2 cups beef broth (such as Pacific Beef Broth)
1⁄4 cup dry red wine
6 sprigs fresh thyme
1 bay leaf
2 sprigs fresh parsley leaves
Ground black pepper

Cheese Croutons:

1 baguette, cut into 1/2-inch slices
4 1⁄2 ounces Swiss cheese, sliced 1/16-inch thick
1 1⁄2 ounces grated Asiago cheese (about 3/4 cup)

Equipment Needed

Heavy-bottomed large (at least 7-quart) Dutch oven
Rimmed baking sheet
Broiler-safe soup bowls or crocks
Baking sheet
Sharp knife
Cutting board
Cheese grater

Instructions

Prepare the Oven: Adjust oven rack to lower-middle position and heat oven to 400°F (200°C). Generously spray the inside of a heavy-bottomed large (at least 7-quart) Dutch oven with nonstick cooking spray.
Initial Onion Roast: Place 3 tablespoons of unsalted butter in the pot and add the sliced yellow onions and 1 teaspoon salt. Cook, covered, for 1 hour. The onions will be moist and slightly reduced in volume.
Continue Onion Roast: Remove the pot from the oven and stir the onions, scraping the bottom and sides of the pot. Return the pot to the oven with the lid slightly ajar (this allows moisture to escape) and continue to cook until the onions are very soft and golden brown, about 1 1/2 to 1 3/4 hours longer. Stir the onions and scrape the bottom and sides of the pot after 1 hour during this stage.
Begin Caramelization on Stovetop: Carefully remove the pot from the oven and place it over medium-high heat on your stovetop.
Evaporate Liquids and Brown Onions: Using oven mitts to handle the pot, cook the onions, stirring frequently and scraping the bottom and sides of the pot, until the liquid evaporates and the onions begin to brown, approximately 15 to 20 minutes. If the onions are browning too quickly, reduce the heat to medium.
Develop the Fond: Continue to cook, stirring frequently, until the pot bottom is coated with a dark crust, about 6 to 8 minutes. Adjust the heat as necessary to prevent burning. Scrape any fond (the browned bits) that collects on your spoon back into the onions – this is flavor gold!
Deglaze First Time: Stir in 1/4 cup water, scraping the pot bottom to loosen the crust. Cook until the water evaporates and the pot bottom has formed another dark crust, about 6 to 8 minutes.
Repeat Deglazing: Repeat the deglazing process of adding 1/4 cup water, scraping, and cooking until evaporated 2 or 3 more times, until the onions are very dark brown and intensely flavorful.
Add Wine and Vinegar: Stir in 1/4 cup dry red wine and 1 tablespoon balsamic vinegar, stirring frequently, until the wine evaporates, about 5 minutes. This adds a crucial layer of acidity that balances the sweetness of the caramelized onions.
Add Broths and Herbs: Stir in 4 cups low sodium chicken broth, 2 cups beef broth, 2 cups water, 6 sprigs of fresh thyme, 1 bay leaf, and 2 sprigs of fresh parsley leaves (tied together with twine or wrapped in cheesecloth for easy removal). Add 1/2 teaspoon salt, scraping up any final bits of browned crust on the bottom and sides of the pot.
Simmer the Soup: Increase the heat to high and bring the soup to a simmer. Then, reduce the heat to low, cover, and simmer for 30 minutes.
Remove Herbs and Season: Remove and discard the herbs. Season the soup with salt and pepper to taste.
Prepare Croutons: While the soup simmers, preheat the oven to 400°F (200°C). Arrange the baguette slices in a single layer on a baking sheet and bake until the bread is dry, crisp, and golden at the edges, about 10 minutes. Set aside.
Assemble for Broiling: Adjust the oven rack 4 to 6 inches from the broiler and heat the broiler. Set heat-safe soup bowls or crocks on a rimmed baking sheet and fill each with about 1 1/2 cups of soup.
Add Croutons and Cheese: Top each bowl with two toasted baguette slices (try not to overlap them). Divide the Swiss cheese slices, laying them in a single layer, if possible, on top of the bread. Sprinkle each serving with about 2 tablespoons grated Asiago cheese.
Broil: Broil until the cheese is well browned and bubbly, about 7 to 10 minutes. Keep a close watch to prevent burning.
Serve: Cool for 5 minutes before serving. The soup will be extremely hot!

Expert Tips & Tricks

Patience is key: Don’t rush the caramelization process. Low and slow is the name of the game for developing deep, rich flavors.
Deglaze Aggressively: Don’t be afraid to really scrape the bottom of the pot when deglazing. Those browned bits are packed with flavor.
Don’t Overlap: Overlapping the bread will cause the cheese to melt into one blob. It’s best if you can lay the cheese flat in a single layer.
Make Ahead: The soup can be made a day or two in advance for even deeper flavor. The flavors meld together beautifully over time.
Broiler Watch: Broilers vary greatly. Keep a close eye on the cheese to prevent burning. If it’s browning too quickly, move the baking sheet further away from the broiler.

Serving & Storage Suggestions

Serve immediately while hot and the cheese is bubbly and melted. The contrast between the warm, savory soup and the rich, cheesy topping is what makes this dish so satisfying.

Leftover soup (without the croutons and cheese) can be stored in an airtight container in the refrigerator for up to 3 days. The soup also freezes well in 2-gallon freezer bags for up to 3 months.

To reheat, gently warm the soup on the stovetop over medium-low heat. When ready to serve, prepare fresh croutons and cheese as directed in the recipe.

Nutritional Information

Nutrient	Amount per Serving	% Daily Value
Calories	727 kcal	N/A
Calories from Fat	144 g	20%
Total Fat	16.1 g	24%
Saturated Fat	8.7 g	43%
Cholesterol	34.9 mg	11%
Sodium	1272.2 mg	53%
Total Carbohydrate	114.2 g	38%
Dietary Fiber	6.7 g	26%
Sugars	11.7 g	N/A
Protein	31.6 g	63%

Note: Nutritional information is an estimate and may vary based on specific ingredients and cooking methods.

Variations & Substitutions

Gluten-Free: Use a gluten-free baguette and ensure all broths are gluten-free.
Vegetarian: Use vegetable broth instead of chicken and beef broth. Consider adding a tablespoon of soy sauce or Worcestershire sauce (check for vegetarian versions) to deepen the umami flavor.
Cheese Options: Gruyere, Emmental, or Provolone can be substituted for Swiss cheese. Parmesan can be used in place of Asiago.
Wine Alternatives: If you don’t want to use wine, you can substitute with more broth or a tablespoon of red wine vinegar.
Sweet Onion Tip: Using sweeter onions? You might want to use a little less Balsamic Vinegar to control the overall sweetness of the soup.

FAQs (Frequently Asked Questions)

Q: Can I use a different type of onion?
A: While yellow onions are recommended for their balance of flavor, you can experiment with other varieties. Avoid overly sweet onions like Vidalia or Walla Walla unless you want a sweeter soup. Red onions can add a slightly sharper flavor.

Q: Why roast the onions instead of caramelizing them on the stovetop?
A: Roasting the onions initially allows for more even cooking and reduces the amount of active stirring required. It’s a more hands-off approach.

Q: Can I make this in a slow cooker?
A: While possible, it’s not recommended as the high heat needed for proper caramelization is difficult to achieve in a slow cooker.

Q: How do I prevent the cheese from burning under the broiler?
A: Keep a close eye on the cheese and adjust the rack position as needed. If the cheese is browning too quickly, move the baking sheet further away from the broiler or reduce the broiler setting to low.

Q: Can I freeze the soup with the croutons and cheese?
A: It’s best to freeze the soup separately from the croutons and cheese. The croutons will become soggy when thawed, and the cheese’s texture may change. Prepare fresh croutons and cheese when serving.

Final Thoughts

This French Onion Soup, inspired by the meticulous methods of Cook’s Illustrated, is a labor of love, but the results are undeniably worth it. The deeply caramelized onions, the rich and flavorful broth, and the bubbly, cheesy topping create a symphony of flavors that will warm you from the inside out. Don’t be intimidated by the length of the recipe; much of the cooking time is passive, allowing you to focus on other things while your kitchen fills with an irresistible aroma. Gather your ingredients, put on some good music, and embark on this culinary adventure. Your family and friends will thank you for it. And please, share your creations and experiences – I’d love to hear about your success and any creative twists you add!

French Onion Soup: the Cook’s Illustrated Way Recipe