Ingredients:

  • 3 tablespoons (45 ml) unsalted butter
  • 2 tablespoons (30 ml) olive oil
  • 3 large yellow onions, thinly sliced (approximately 1.5 kg / 3.3 lbs)
  • 1 teaspoon (5 ml) granulated sugar
  • 1/2 teaspoon (2.5 ml) kosher salt
  • 1/4 teaspoon (1.25 ml) black pepper
  • 1 tablespoon (15 ml) balsamic vinegar
  • 6 cups (1.4 liters) good quality beef broth
  • 1 cup (240 ml) dry red wine (like a Cabernet Sauvignon or Merlot)
  • 1 tablespoon (15 ml) Worcestershire sauce
  • 1 teaspoon (5 ml) dried thyme
  • 1 bay leaf
  • 1/4 cup (30 g) all-purpose flour
  • 1/4 cup (60 ml) cold water
  • Salt and pepper to taste
  • 6 cups (approx. 200g) cubed day-old baguette or French bread (roughly 1-inch cubes)
  • 4 tablespoons (60 ml) melted unsalted butter
  • 1/2 teaspoon (2.5 ml) garlic powder
  • 1/4 teaspoon (1.25 ml) dried parsley
  • 1/4 teaspoon (1.25 ml) kosher salt
  • 1/4 teaspoon (1.25 ml) black pepper
  • 8 ounces (225g) Gruyère cheese, grated

Instructions:

  1. Melt butter and olive oil in a large Dutch oven or pot. Add onions, sugar, salt, and pepper. Cook over medium-low heat, stirring occasionally, until deeply caramelized and golden brown (about 45-60 minutes). Stir in balsamic vinegar during the last few minutes.
  2. Add beef broth, red wine, Worcestershire sauce, thyme, and bay leaf to the pot with the onions. Bring to a simmer and cook for 15 minutes to allow flavors to meld.
  3. In a small bowl, whisk together flour and cold water to create a slurry. Slowly pour the slurry into the simmering broth, whisking constantly to avoid lumps. Cook until the broth thickens slightly (about 5 minutes). Remove bay leaf. Season with salt and pepper to taste.
  4. Preheat oven to 375°F (190°C). In a large bowl, toss the bread cubes with melted butter, garlic powder, parsley, salt, and pepper. Spread the croutons in a single layer on a baking sheet. Bake for 8-10 minutes, or until golden brown and crispy.
  5. Pour the onion soup mixture into the prepared 9x13 inch baking dish. Sprinkle evenly with grated Gruyère cheese. Top with the toasted croutons.
  6. Bake in the preheated oven for 20-25 minutes, or until the cheese is melted, bubbly, and lightly browned.
  7. Let the casserole rest for 10 minutes before serving.