Ingredients:

  • 4 large Yellow Onions, thinly sliced
  • 3 Tbsp Unsalted Butter
  • 1 Tbsp Olive Oil
  • 1/2 tsp Granulated Sugar (Optional)
  • 1 tsp Dry Thyme
  • Salt and Black Pepper, to taste
  • 1/2 cup Dry Sherry or Vermouth
  • 3 cups High-Quality Beef Stock
  • 1 Tbsp All-Purpose Flour
  • 4 Boneless, Skinless Chicken Breasts (approx. 6 oz each)
  • 4 slices Day-Old Baguette (approx. 1-inch thick)
  • 4 oz Gruyère Cheese, freshly grated

Instructions:

  1. Sauté Aromatics: Heat the butter and olive oil in a large, oven-safe skillet over medium-low heat. Add the sliced onions, sugar (if using), and a pinch of salt.
  2. Caramelize Slowly: Cook the onions, stirring occasionally, for 40 to 50 minutes until they achieve a deep, dark mahogany colour. The heat must be kept low to prevent burning.
  3. Add Thyme: Stir in the dried thyme during the last 10 minutes of cooking the onions. Remove the caramelized onions from the skillet and set aside.
  4. Sear Chicken: Pat the chicken breasts thoroughly dry and season liberally with salt and pepper. Add 1 Tbsp of oil to the skillet, increase heat to medium-high, and sear the chicken for 3–4 minutes per side until deeply golden brown. Remove the chicken and set aside.
  5. Deglaze and Build Sauce: Reduce the heat to medium. Pour the sherry (or wine) into the pan, scraping up all the savory browned bits (fond) from the bottom of the skillet. Reduce the liquid by half (about 2 minutes).
  6. Thicken: Sprinkle the flour over the liquid and whisk for 1 minute. Pour in the beef stock and bring the sauce to a gentle simmer. Taste and adjust salt and pepper.
  7. Recombine: Stir the caramelized onions back into the simmering sauce.
  8. Assemble: Return the seared chicken breasts to the pan, nesting them into the onion sauce. Place one slice of baguette atop each chicken breast.
  9. Gratinée: Distribute the freshly grated Gruyère evenly over the bread slices and sauce. Transfer the skillet to a preheated oven (375°F / 190°C).
  10. Bake: Bake for 18–20 minutes, or until the cheese is bubbling, golden brown, and the chicken registers an internal temperature of 165°F (74°C).
  11. Serve: Remove from the oven and allow the dish to rest in the skillet for 5 minutes before serving.