Makes approximately 8 servings ⋅ Adapted from

  • Cooking spray
  • 10 cups vertically sliced onions (from 5 onions)
  • 2 tablespoons unsalted butter, melted
  • ½ teaspoon black pepper
  • 6 cups unsalted beef stock
  • ¼ cup dry Marsala wine
  • 1 teaspoon chopped fresh thyme, plus more for garnish
  • ¾ teaspoon kosher salt
  • 12 ounces whole-wheat baguette (see Tip), cut into 16 slices
  • 5 ounces Gruyère cheese, shredded (about 1 1/4 cups)
  1. Coat a 4-quart slow cooker with cooking spray. Stir together the onions, butter and pepper in the slow cooker; cover and cook on LOW until the onions are very soft and deep golden brown, about 10 hours.

  2. Stir in the stock, marsala, thyme and salt. Cover and cook on HIGH until the flavors are blended, about 2 hours.

  3. Preheat the broiler with the oven rack 6 inches from the heat. Place the baguette slices on a baking sheet, and sprinkle evenly with the Gruyère. Broil until the Gruyère melts, 2 to 3 minutes. Ladle the soup into bowls. Top with the cheese toasts. Garnish with the additional thyme, if desired.