French Country Slow Cooker Chicken

1 med onion, chopped
4 carrots, cut into 1/4 inch slices
4 ribs celery, cut into slices
6-8 boneless skinless chicken breasts (about 1 1/2 - 2 lbs)
1 tsp dried tarragon leaves
salt and black pepper
1 can cream of chicken soup
1 envelope dry onion soup mix
1/3 white wine or apple juice
2 Tbsp cornstarch
Hot cooked rice

Place onion, carrots and celery in slow cooker. Arrange chicken over vegetables. Sprinkle with seasonings. Pour soup over chicken. Sprinkle with soup mix. Cover and cook in high 3-4 hours, stirring once during cooking. Blend wine and cornstarch in a small bowl until smooth. Stir into slow cooker. Cook uncovered 15 minutes or until sauce thickens. Serve over rice.