1.Place The Chicken In A 5-Qt. Slow Cooker. In A Small Bowl, Combine The Soup, Mushrooms, Sherry Or Broth, Butter, Tarragon, Worcestershire Sauce And Garlic Powder; Pour Over Chicken. Cover And Cook On Low For 4-5 Hours Or Until Chicken Juices Run Clear. 2.Remove Chicken And Keep Warm. Place The Flour In A Small Saucepan; Gradually Whisk In Cooking Liquid Until Blended. Bring To A Boil; Cook And Stir For 2 Minutes Or Until Thickened. Serve Over Chicken.