Ingredients:

  • 3 lbs (1.36 kg) yellow onions, thinly sliced
  • 4 tbsp (57g) unsalted butter
  • 1 tbsp (15 ml) olive oil
  • 1 tsp (5 ml) granulated sugar
  • 1/2 tsp (2.5 ml) dried thyme
  • 1/4 tsp (1.25 ml) dried bay leaf
  • 8 cups (1.9 L) beef broth (low sodium preferred)
  • 1 cup (237 ml) dry red wine (such as Burgundy or Cabernet Sauvignon – optional)
  • 1 tbsp (15 ml) Worcestershire sauce
  • Salt and freshly ground black pepper to taste
  • 1 baguette, sliced into 1-inch thick rounds
  • 4 oz (113g) Gruyère cheese, shredded

Instructions:

  1. Melt butter and olive oil in a large skillet over medium heat. Add onions and sugar. Cook, stirring occasionally, until onions are deeply golden brown and caramelized, about 30-40 minutes. Watch carefully to prevent burning.
  2. Transfer the caramelized onions to the slow cooker. Add beef broth, red wine (if using), Worcestershire sauce, thyme, and bay leaf. Season with salt and pepper.
  3. Cover and cook on low for 6-8 hours, or on high for 3-4 hours.
  4. While the soup is cooking, preheat oven to 375°F (190°C). Arrange baguette slices on a baking sheet. Bake for 5-7 minutes per side, or until golden brown and crispy.
  5. Preheat broiler. Ladle soup into oven-safe bowls. Top each bowl with a few croutons and a generous amount of shredded Gruyère cheese. Broil for 2-3 minutes, or until cheese is melted and bubbly.
  6. Carefully remove from the oven (if broiling) and serve immediately. Garnish with fresh parsley (optional).