Ingredients:

  • 3 lbs yellow onions, halved and thinly sliced
  • 4 tbsp unsalted European-style butter, cubed
  • 1 tbsp extra virgin olive oil
  • 1 tsp granulated sugar
  • 1/2 tsp kosher salt
  • 6 cups high-quality beef bone broth
  • 1/2 cup dry Sherry
  • 2 tbsp Worcestershire sauce
  • 1 tbsp balsamic vinegar
  • 3 sprigs fresh thyme
  • 2 dried bay leaves
  • 1/2 tsp black pepper
  • 1 French baguette, cut into 1-inch thick rounds
  • 2 cups Gruyère cheese, freshly shredded
  • 1/2 cup Parmigiano-Reggiano, finely grated
  • 1 clove garlic, peeled

Instructions:

  1. Halve your 3 lbs of yellow onions and slice them into thin half moons.
  2. Place the sliced onions in the slow cooker and toss with 1 tbsp extra virgin olive oil, 1 tsp granulated sugar, and 1/2 tsp kosher salt.
  3. Top the onions with 4 tbsp cubed unsalted butter. Cover and cook on low for 10 hours.
  4. Stir in 6 cups beef bone broth, 1/2 cup dry Sherry, 2 tbsp Worcestershire sauce, and 1 tbsp balsamic vinegar. Add the 3 sprigs of thyme, 2 bay leaves, and 1/2 tsp black pepper.
  5. Cover again and cook on low for another 2 hours until the flavors are fully married and the broth is dark.
  6. Preheat your oven to 400°F. Cut the French baguette into 1 inch thick rounds and toast for 5 minutes until they are crisp and lightly golden. Remove the bread and rub the 1 clove of peeled garlic over the surface of each warm slice.
  7. Ladle the hot soup into oven safe bowls. Place two slices of toasted bread on top of each bowl, ensuring they cover most of the surface. Generously pile 2 cups shredded Gruyère and 1/2 cup Parmigiano Reggiano over the bread.
  8. Place the bowls on a baking sheet and broil for 3 minutes until the cheese is bubbling and brown spots appear.
  9. Let the bowls sit for 2 minutes before serving.