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Velvety Caramelized Onion Soup with Vinegar Brightness

This onion soup is made by slowly caramelizing sliced onions until deeply browned, then simmering them in flavorful broth. The soup is finished with melting cheese, herbs, and a splash of apple cider vinegar, resulting in a rich, smooth, and aromatic final dish with a slightly tangy finish.
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Prep Time 15 minutes
Cook Time 45 minutes
Total Time 1 hour
Servings: 4
Course: Main Course
Cuisine: Comfort Food
Calories: 330
Ingredients Equipment Method Notes

Ingredients
  

  • 4 large yellow onions thinly sliced
  • 2 tablespoons olive oil
  • 2 cloves garlic minced
  • 4 cups beef or vegetable broth
  • 1 cup shredded Gruyère cheese
  • 1 tablespoon apple cider vinegar
  • 1 bay leaf bay leaf
  • 1 teaspoon fresh thyme or ½ teaspoon dried thyme
  • to taste salt and pepper

Equipment

  • Large heavy-bottomed pot or Dutch oven
  • Wooden Spoon or Heat-Resistant Spatula

Method
 

  1. Heat a large heavy-bottomed pot over medium heat and add the olive oil. Once shimmering, add the sliced onions and a pinch of salt. Cook slowly, stirring frequently, until the onions are deeply golden and caramelized, about 30-40 minutes, until they smell sweet and look rich brown.
  2. Add the minced garlic to the caramelized onions and cook for another 1-2 minutes until fragrant and softened, with a slight sizzle and aroma of garlic filling the air.
  3. Pour in the broth and stir well, scraping up any browned bits from the bottom. Add the bay leaf and thyme, then bring the mixture to a gentle simmer. Let it cook uncovered for about 15 minutes to develop deeper flavor.
  4. Remove the bay leaf and stir in the apple cider vinegar, balancing the sweetness with a bright, tangy note. Season with salt and pepper to taste, adjusting as needed.
  5. Preheat your oven's broiler and ladle the soup into oven-safe bowls. Top each with a generous handful of shredded cheese, spreading evenly over the surface.
  6. Place the bowls on a baking sheet and broil until the cheese is melted, bubbly, and lightly golden, about 2-3 minutes. Keep a close eye to prevent burning.
  7. Carefully remove the bowls from the oven and let cool slightly. Serve hot, with the cheesy topping, fragrant broth, and caramelized onions visible in each bowl—a comforting, rich-toasted crust with tender onions inside.

Notes

For a vegetarian version, replace beef broth with vegetable broth. To add a crunch, serve with toasted baguette slices on top or on the side.