Quick Chicken Fricassee

From America's Test Kitchen episode: Simply Chicken.

Serves 4 to 6

Two tablespoons of chopped fresh parsley leaves may be substituted for the tarragon in this recipe.

2 pounds boneless, skinless chicken breasts, thighs, or a combination
Table salt and ground black pepper
1tablespoon unsalted butter
1tablespoon olive oil
1pound cremini mushrooms, stems trimmed, caps wiped clean and cut into 1/4-inch slices
1 medium onion, chopped fine (about 1 cup)
1/4cup dry white wine
1tablespoon unbleached all-purpose flour
1 medium garlic clove, minced or pressed through garlic press (about 1 teaspoon)
1 1/2cups low-sodium chicken broth
1/3cup sour cream
1 egg yolk
1/2teaspoon freshly grated nutmeg
2teaspoons juice from 1 lemon
2teaspoons minced fresh tarragon (see note)

1. Pat chicken dry with paper towels and season with 1 teaspoon salt and ½ teaspoon pepper. Heat butter and oil in 12-inch skillet over medium-high heat. When foaming subsides, place chicken in skillet and cook until browned, about 4 minutes. Flip chicken and continue to cook until browned on second side, about 4 minutes longer. Transfer chicken to large plate.
2. Add mushrooms, onion, and wine to now-empty skillet and cook, stirring occasionally, until liquid has evaporated and mushrooms are browned, 8 to 10 minutes. Add flour and garlic; cook, stirring constantly, 1 minute. Add broth and bring mixture to boil, scraping bottom of pan with wooden spoon to loosen browned bits. Add chicken and any accumulated juices to skillet. Reduce heat to medium-low, cover, and simmer until instant-read thermometer registers 160 degrees when inserted in breasts and 175 degrees when inserted in thighs, 5 to 10 minutes.
3. Transfer chicken to clean platter and tent loosely with foil. Whisk sour cream and egg yolk together in medium bowl. Whisking constantly, slowly stir ½ cup sauce into sour cream mixture. Stirring constantly, slowly pour sour cream mixture into simmering sauce. Stir in nutmeg, lemon juice, and tarragon; return to simmer. Season to taste with salt and pepper. Pour sauce over chicken and serve.

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