According to JS Online, the site where K found the Chicken Breasts with Mustard-Cider Sauce, this recipe hails from America's Test Kitchen: Let's Get Cooking. It's good as is. Frankly, I don't know how you can go wrong with a sauce containing: apple cider, apple cider vinegar, whole-grain mustard, butter, and shallots. K served it with some angel hair pasta with olive oil and cheese, which complemented the vinegary sauce.
To see the chicken recipe in outline form, click on the link below.
Chicken Breasts with Mustard-Cider Sauce
½ cup flour
4 boneless, skinless chicken breasts (6 to 8 ounces each)
¼ teaspoon salt, plus more for seasoning (divided)
Dash of pepper
3 tablespoons vegetable oil (divided)
1 shallot, minced
1 ¼ cups apple cider
2 tablespoons cider vinegar
3 tablespoons butter
2 tablespoons minced fresh parsley
2 teaspoons whole-grain mustard
1) Preheat oven to 200 degrees.
2) Place flour in a wide, shallow dish.
3) Wash and dry chicken.
4) Pound down thick ends of the chicken breasts until pieces are a uniform thickness for even cooking.
5) Pat dry, season lightly with salt and pepper, then dredge with flour.
6) Shake off excess.
7) Heat 2 tablespoons oil in a 12-inch skillet over medium-high heat until just smoking.
8) Add chicken pieces and cook until light golden brown on both sides, about 10 minutes.
9)Transfer pieces to a plate and keep warm in preheated oven.
10) Add remaining 1 tablespoon oil to skillet over medium-high heat and add minced shallot with ¼ teaspoon salt.
11) Cook until softened, about 2 minutes.
12) Stir in apple cider and cider vinegar, scraping up the browned bits on pan bottom.
13) Simmer until sauce has reduced and turns slightly syrupy, about 8 minutes.
14) Stir in any accumulated juices from plate with chicken.
15) Turn heat to low and whisk in butter, a tablespoon at a time.
16) Remove from heat.
17) Stir in parsley and mustard.
18) Season with salt and pepper to taste, if needed.
19) Spoon sauce over chicken to serve.