How to Make It
Heat a large skillet over medium heat. Add oil to pan; swirl to coat. Sprinkle chicken with salt and pepper; cook 3 minutes on each side. Place chicken on a platter.
Return pan to medium heat. Add shallots; sauté 1 minute. Sprinkle flour over shallots; cook 1 minute, stirring constantly. Add wine; bring to a boil. Cook 1 minute, scraping pan to loosen browned bits. Remove from heat; stir in sour cream and mustard. Return chicken and juices to pan. Sprinkle with tarragon.