Rinse turkey breast, drain well and pat dry with paper towel. Place, skin side up in slow cooker. Brush with butter. Sprinkle with parsley, tarragon and paprika. Add wine, salt and pepper. Cover and cook on high setting for 1 hour, then turn to low setting for 6 to 7 hours. Internal temperature of breast should reach 170 when done.
Slice and serve with mushroom sauce.
Sauce: Strain drippings from slow cooker into large liquid measure. Spoon off fat. Add mushrooms to drippings and enough water to make 1 - 3/4 cupfuls. Dissolve cornstarch in water or wine and stir into drippings. Pour into saucepan, add tarragon and season to taste with salt and pepper. Cook over medium to low heat, stirring constantly, until thickened and clear.