Ingredients:

  • 3 lbs (1.36 kg) yellow onions, thinly sliced
  • 4 tbsp (56g) unsalted butter
  • 2 tbsp (30 ml) olive oil
  • 1 tsp granulated sugar
  • 1/2 tsp dried thyme
  • 1/4 tsp dried bay leaf
  • 8 cups (1.9 L) beef broth (low-sodium preferred)
  • 1 cup (240 ml) dry red wine (Burgundy or Cabernet Sauvignon recommended, optional)
  • 2 tbsp (30 ml) Worcestershire sauce
  • Salt and freshly ground black pepper to taste
  • 1 baguette, sliced into 1-inch rounds
  • 4 tbsp (56g) unsalted butter, melted
  • 4 cloves garlic, minced
  • 8 oz (225g) Gruyère cheese, shredded

Instructions:

  1. Thinly slice the onions.
  2. For a deeper flavor, caramelize the onions in a large skillet with butter and olive oil over medium-low heat, stirring occasionally, until golden brown and sweet (about 30-45 minutes). Add sugar, thyme and bay leaf during the last 5 minutes of caramelization.
  3. Place the onions (caramelized or raw) in the slow cooker.
  4. Pour in the beef broth, red wine (if using), and Worcestershire sauce. Season with salt and pepper.
  5. Cover and cook on low for 8-10 hours or on high for 4-6 hours.
  6. While the soup is cooking, preheat oven to 375°F (190°C). In a small bowl, mix melted butter with minced garlic. Brush baguette slices with garlic butter. Arrange on a baking sheet and bake until golden brown and crispy (about 8-10 minutes).
  7. Ladle soup into oven-safe bowls. Top each bowl with croutons and a generous amount of shredded Gruyère cheese. Broil in the oven until the cheese is melted and bubbly (about 2-3 minutes). Watch carefully to prevent burning!
  8. Serve immediately, being careful as the bowls will be hot.