Caramelized French Onion Soup (Printable)

Rich French onion soup with caramelized onions and cheesy sourdough crostini, perfect for cozy meals.

# What Goes In:

→ For the Soup

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
13 - Salt and pepper to taste

→ For the Sourdough Gruyère Crostini

14 - 1 small sourdough baguette, sliced into 1/2-inch rounds
15 - 2 tablespoons olive oil
16 - 1 cup Gruyère cheese, grated
17 - 1/2 cup Parmesan cheese, grated

# How to Make It:

01 - In a large heavy-bottomed pot, melt butter with 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 the minced garlic and cook for 1 minute until fragrant.
04 - Sprinkle flour over onions and cook, stirring constantly, for 2 minutes to cook out the raw flour taste.
05 - Pour in white wine, scraping up any browned bits from the pot bottom. Simmer for 2 to 3 minutes to reduce the wine.
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. 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 bread with Gruyère and Parmesan cheese. Return to oven and bake until cheese is melted and bubbly, 3 to 4 minutes.
09 - Ladle soup into oven-safe bowls, place crostini on top, and serve immediately while hot.

# Expert Tips:

01 -
  • The caramelized onions transform into something almost sweet and jammy, nothing like raw onions—it's a complete flavor metamorphosis.
  • Those crispy, cheese-topped crostini pieces float on the soup like little islands of comfort, and the contrast between the creamy broth and crunchy bread is honestly addictive.
  • You can make the soup ahead, which means less stress and more time to actually enjoy it with people around your table.
02 -
  • Don't rush the caramelization—I learned this the hard way by turning up the heat to speed things along, which just burned the bottom layer while the rest stayed pale and sweet, ruining the entire batch.
  • The white wine matters more than you'd think; cooking wine or something overly acidic will leave a harsh taste, so use something you'd actually drink.
  • Make the crostini right before serving—if they sit too long, even in a warm soup, they become soggy and lose that satisfying crunch that makes people reach for seconds.
03 -
  • The secret to consistent caramelization is using a heavy-bottomed pot and resisting the urge to turn up the heat—medium heat takes longer but delivers that even, deep color that thinner pots struggle to achieve.
  • Grate your cheese fresh if possible; pre-shredded cheese has anti-caking agents that prevent it from melting as smoothly and luxuriously as freshly grated.
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