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Classic French Onion Soup

This French Onion Soup is built on the slow caramelization of sweet onions, which develop a deep, rich flavor through patience and gentle cooking. The onions are simmered in a hearty broth until tender and sweet, then topped with toasted bread and bubbling Gruyère cheese for a comforting, visually appealing final dish. The result is a thick, fragrant soup with a glossy, cheesy crust and tender caramelized onions visible through the broth.
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Prep Time 15 minutes
Cook Time 1 hour 15 minutes
Total Time 1 hour 30 minutes
Servings: 4
Course: Main Course
Cuisine: French
Calories: 350
Ingredients Equipment Method Notes

Ingredients
  

  • 4-5 large yellow onions peeled and thinly sliced
  • 3 tbsp unsalted butter for caramelizing onions
  • 4 cups beef broth or vegetable/mushroom broth for vegetarian
  • 1 tbsp dry sherry optional, for lift and brightness
  • 4 slices French baguette sliced into 1-inch pieces, toasted
  • 1 1/2 cups Gruyère cheese grated
  • 2 sprigs fresh thyme or bay leaf, added during simmering
  • to taste salt and pepper

Equipment

  • Heavy-bottomed pot
  • Sharp knife
  • Wooden spoon
  • Oven-safe bowls or crocks
  • Baking sheet
  • Toaster or oven

Method
 

  1. Begin by peeling and thinly slicing the onions, aiming for uniform slices to ensure even caramelization.
  2. Heat your heavy-bottomed pot over medium-low heat, then add the butter and a splash of olive oil to prevent burning. Let the butter melt and foam gently.
  3. Add the sliced onions to the pot, sprinkle with a pinch of salt, and stir gently to coat. Cook slowly, stirring every 10 minutes, for about 45-60 minutes, until the onions are deeply golden, fragrant, and slightly sticky, turning a rich amber color.
  4. If the onions start to stick or darken too quickly, add a small splash of water or broth to deglaze the pan and scrape up flavorful caramelized bits from the bottom. Continue cooking until the onions are uniformly deep amber.
  5. Pour in the broth and stir in the dry sherry and sprigs of thyme. Bring the mixture to a gentle simmer and cook uncovered for another 15 minutes to let flavors meld. Taste and season with salt and pepper as needed, removing the herbs before serving.
  6. Preheat your oven’s broiler. Slice the baguette into 1-inch thick pieces and toast in the oven until golden and crispy, about 3-4 minutes per side.
  7. Ladle the hot onion broth into oven-safe bowls or crocks, then place a toasted bread slice on top of each. Generously sprinkle grated Gruyère cheese over the bread, covering the surface evenly.
  8. Place the bowls on a baking sheet and broil in the oven until the cheese is bubbly and golden brown, about 2-4 minutes. Keep a close eye to prevent burning.
  9. Carefully remove the bowls from the oven, let them sit for a minute to cool slightly, then serve immediately while the cheese is gooey and bubbling, and the broth is fragrant and warm.

Notes

Patience during caramelization is key. Low and slow is your best friend for building deep, sweet onion flavor. For a vegetarian version, swap the broth and consider boosting umami with soy sauce or miso.