Instructions

1. 1

   In a large, oven-safe skillet over medium-low heat, melt the butter. Add the thinly sliced onions, granulated sugar, 1/4 teaspoon salt, and 1/4 teaspoon black pepper.

2. 2

   Cook, stirring occasionally, for 15-20 minutes, or until the onions are deeply golden brown and very soft. If they start to stick, add a tablespoon of water or broth.

3. 3

   Stir in the dried thyme. Remove onions from the skillet and set aside.

4. 4

   Pat the chicken breasts dry with paper towels. Season both sides generously with salt and pepper.

5. 5

   Add olive oil to the same skillet over medium-high heat. Once hot, add the chicken breasts and sear for 3-4 minutes per side, until golden brown.

6. 6

   Remove chicken from the skillet and set aside with the onions.

7. 7

   Reduce heat to medium. If using, pour in the dry sherry or white wine, scraping up any browned bits from the bottom of the skillet. Let it simmer for 1-2 minutes until slightly reduced.

8. 8

   Sprinkle the flour into the skillet and whisk continually for 1 minute to cook out the raw flour taste.

9. 9

   Slowly pour in the beef broth, whisking constantly to prevent lumps. Bring the sauce to a simmer and cook for 2-3 minutes, or until it has slightly thickened.

10. 10

    Taste and adjust seasoning with salt and pepper if needed.

11. 11

    Return the caramelized onions to the skillet, stirring them into the sauce. Nestle the seared chicken breasts into the onion-sauce mixture.

12. 12

    Preheat your oven broiler. Sprinkle the shredded Gruyère and provolone cheeses evenly over the chicken breasts and onions.

13. 13

    Transfer the skillet to the preheated broiler. Broil for 3-5 minutes, watching carefully, until the cheese is melted, bubbly, and beautifully golden brown.

14. 14

    Carefully remove the skillet from the oven. Garnish with fresh chopped parsley and serve immediately.