Caramelized French Onion Soup (Printer-Friendly)

Hearty French onion soup with slow-caramelized onions and cheesy sourdough crostini.

# What You'll Need:

→ Soup Base

01 - 6 large yellow onions, thinly sliced
02 - 3 tablespoons unsalted butter
03 - 1 tablespoon olive oil
04 - 1 teaspoon sugar
05 - 1 teaspoon salt
06 - 1/2 teaspoon freshly ground black pepper
07 - 2 cloves garlic, minced
08 - 2 tablespoons all-purpose flour
09 - 1/2 cup dry white wine
10 - 6 cups beef broth
11 - 2 sprigs fresh thyme
12 - 1 bay leaf

→ Sourdough Gruyere Crostini

13 - 1 small sourdough baguette, sliced into 1/2-inch rounds
14 - 2 tablespoons olive oil
15 - 1 cup Gruyere cheese, grated
16 - 1/2 cup Parmesan cheese, grated

# Method:

01 - In a large heavy-bottomed pot, melt butter and olive oil over medium heat.
02 - Add sliced onions, sugar, salt, and pepper. Cook, stirring frequently, for 35 to 45 minutes until onions are deep golden and caramelized.
03 - Stir in minced garlic and cook for 1 minute.
04 - Sprinkle flour over onions and cook, stirring constantly, for 2 minutes.
05 - Pour in white wine, scraping up any browned bits from the bottom of the pot. Simmer for 2 to 3 minutes to reduce.
06 - Add beef broth, thyme sprigs, and bay leaf. Bring to a gentle boil, then reduce heat and simmer uncovered for 25 to 30 minutes. Adjust seasoning with salt and pepper to taste. Remove and discard thyme sprigs and bay leaf.
07 - While soup simmers, preheat oven to 400 degrees Fahrenheit. Arrange baguette slices on a baking sheet, brush with olive oil, and toast for 5 to 7 minutes until golden brown.
08 - Top toasted baguette slices with grated Gruyere and Parmesan cheese. Return to oven and bake until cheese is melted and bubbly, approximately 3 to 4 minutes.
09 - Ladle soup into oven-safe bowls, place crostini on top, and optionally broil for 1 to 2 minutes for extra caramelization. Serve immediately while hot.

# Expert Suggestions:

01 -
  • It's the kind of soup that tastes like you spent all day cooking when you really just needed patience and good timing.
  • Those crispy, cheesy crostini on top turn something humble into something that feels like a proper occasion.
02 -
  • Caramelizing onions is meditative, not quick—rushing it with higher heat gives you brown onions, not caramelized ones, and they're not the same thing.
  • The flour will seem like an odd step, but it prevents the soup from breaking if you're planning to broil it with crostini on top, and it adds a subtle richness that makes people ask what your secret ingredient is.
03 -
  • If you're making this ahead, caramelize the onions and make the broth the day before, then reheat and assemble everything fresh—the flavors actually deepen overnight.
  • A splash of brandy or sherry stirred in just before serving adds sophistication without tasting like you tried too hard; it's the kind of thing your friends won't quite be able to name but will definitely taste.
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