Ingredients:

  • 1.36 kg yellow onions, thinly sliced
  • 56 g unsalted butter
  • 15 ml olive oil
  • 5 g granulated sugar
  • 6 g salt
  • 3 g black pepper
  • 1.9 L low-sodium beef broth
  • 16 g all-purpose flour
  • 30 ml apple cider vinegar
  • 9 g garlic, minced
  • 1 g dried thyme
  • 2 bay leaves
  • 1 French baguette, sliced into 1-inch rounds
  • 225 g Gruyère cheese, shredded
  • 50 g Parmesan cheese, finely grated

Instructions:

  1. Preheat the oven to 180°C (350°F).
  2. Melt 56 g unsalted butter and 15 ml olive oil in a Dutch oven over medium heat.
  3. Add 1.36 kg thinly sliced yellow onions and stir to coat.
  4. Sprinkle with 5 g granulated sugar and 6 g salt, then reduce heat to medium-low.
  5. Cook the onions for 45 to 60 minutes, stirring every 10–15 minutes, until they transition to a deep, mahogany brown.
  6. Increase the heat to medium and stir in 9 g minced garlic and 1 g dried thyme; cook for 1 minute until fragrant.
  7. Sprinkle 16 g all-purpose flour over the onions and stir constantly for 2 minutes to cook out the raw flour taste.
  8. Slowly pour in 1.9 L low-sodium beef broth and 30 ml apple cider vinegar, scraping the bottom of the pot to release the browned bits.
  9. Add 2 bay leaves, bring to a simmer, then reduce heat to low and bubble gently for 30 minutes.
  10. While the soup simmers, place the sliced French baguette rounds on a baking sheet and toast in the oven for 5 minutes per side.
  11. Ladle the soup into oven-safe crocks.
  12. Place one toasted baguette slice on top of each bowl, then top with 225 g shredded Gruyère and 50 g finely grated Parmesan divided evenly among the servings.
  13. Place the crocks under the broiler for 2–4 minutes until the cheese is bubbling and browned around the edges.