Ingredients:

• 2 tablespoons unsalted butter
• 4 tablespoons extra virgin olive oil, divided
• 4 large white onions, halved and thinly sliced
• 1 teaspoon sugar
• 2 teaspoons fresh thyme
• 1 tablespoon balsamic vinegar
• 1 cup beef broth, divided
• 3 cloves garlic, minced
• 4 boneless, skinless chicken breasts
• 1 ½ cups Gruyère cheese, grated
• ½ cup Parmesan cheese, freshly grated
• Kosher salt and black pepper, to taste

Instructions:

1. Preheat & Prepare
   • Preheat the oven to 400°F.
   • Lightly grease a 9x13-inch baking dish with butter or nonstick spray.
2. Caramelize the Onions
   • Heat 2 tablespoons butter and 2 tablespoons olive oil in a large skillet over medium-high heat.
   • Add the sliced onions and spread them evenly in the pan. Cook, stirring occasionally, until softened.
   • Sprinkle with salt, sugar, and thyme. Reduce heat to medium if needed to prevent burning.
   • Continue cooking, stirring occasionally, until onions become jammy and deep golden brown.
   • Add ½ cup beef broth as needed to prevent drying out.
   • Stir in balsamic vinegar, scraping up any browned bits from the pan.
   • Add garlic and cook for another 30 seconds to 1 minute, then remove from heat.
3. Prepare the Chicken
   • Slice a pocket into each chicken breast without cutting all the way through.
   • Stuff each pocket with about 2 tablespoons of caramelized onions and a portion of both cheeses. Secure with toothpicks.
4. Assemble & Sear the Chicken
   • Spread the remaining caramelized onions in the greased baking dish. Stir in the remaining ½ cup beef broth.
   • Heat the remaining 2 tablespoons olive oil in a clean skillet over medium-high heat.
   • Season the stuffed chicken breasts with salt and pepper.
   • Sear for about 4 minutes per side, until golden brown (they don’t need to be fully cooked).
5. Bake
   • Place the seared chicken on top of the onions in the baking dish.
   • Spoon some of the onion mixture over each chicken breast and top with any remaining cheese.
   • Bake for 15-20 minutes or until the chicken is cooked through.
6. Serve & Enjoy
   • Remove toothpicks before serving. Enjoy warm with your favorite side dish!