2 lbs boneless, skinless chicken breasts or thighs
2 cups beef broth
1 cup swiss chese, grated
1/3 cup EVOO, divided
2 tbsp all-purpose flour
2 tsp balsamic vinegar
1/2 tsp dried thyme
1/2 tsp dried sage
Kosher salt and fresh ground pepper, to taste
Preheat oven to 350 degrees F
Heat 2 tbsp EVOO in a large, oven-proof pan or skillet over medium heat. Add onions, season with salt and cook, stirring occasionally, for 15-20 minutes, or until softened and caramelized
Add balsamic vinegar and cook for another 3-5 minutes or until darkened, but not burned
Remove onions from heat and transfer to a medium bowl
Heat remaining EVOO in skillet and raise heat to medium-high
Season chicken breasts with salt, pepper, thyme and sage, then place in skillet and sear on both sides until golden brown. Remove chicken from heat and set aside
Pour beef broth into skillet and bring mixture to a boil, scraping up stuck bits from the bottom of the pan
Return heat to medium-low and whisk in flour, stirring until smooth. Cook for 5-7 minutes, or until mixture has thickened. Taste and adjust seasoning, if necessary
Return chicken and onions to pan, stir together with beef gravy, then top with grated swiss cheese
Transfer skillet to oven and cook until cheese is melted and bubbly, and chicken is cooked through