INGREDIENTS

4 boneless, skinless chicken breast halves, about 8 ounces each
Kosher salt
Freshly ground black pepper
1 tablespoon olive oil
1 cup low-sodium chicken broth
3/4 cup dry white wine
1 sprig fresh thyme
2 tablespoons unsalted butter (1/4 stick), at a cool room temperature
2 tablespoons whole-grain mustard
1 tablespoon all-purpose flour
2 tablespoons finely chopped flat-leaf parsley

DIRECTIONS

1. Heat the oven to 425°F and arrange a rack in the middle. Season the chicken breasts all over with salt and black pepper. 
2. Set a large, heavy, ovenproof frying pan or cast-iron skillet over medium-high heat. When it’s hot, add the oil and swirl to coat the bottom of the pan. Add the chicken, presentation (i.e., smooth) side down, and cook until browned, about 4 minutes. Using tongs, turn the chicken over and put the frying pan in the oven.  Bake until the chicken is cooked through but still juicy, about 6 minutes. Transfer to a warm platter and let sit for about 10 minutes, while you make the sauce.
3. Return the frying pan to the stovetop over medium-high heat. Add the broth, wine, and thyme sprig. Bring to a boil, scraping the bottom of the pan to loosen any browned bits. Cook for 5 minutes. 
4. In a small bowl, stir together the butter, mustard, and flour to form a paste. Whisk into the liquid in the pan. Cook, stirring constantly with a whisk, until the mixture thickens, about 2 minutes. Remove from the heat and stir in the parsley. Serve the chicken on warmed plates, ladled with the sauce.