Cooking Method:

1. In a slow cooker,combine chicken and onion.
2. In a small mixing bowl,combine chicken broth,2 tablespoons Dijon mustard,dried tarragon.Stir well and season with salt and black pepper.
3. Pour tarragon mixture over chicken.Stir well to combine.
4. Cover slow cooker and cook on low-heat setting for 5 1/2 hours.
5. Using a slotted spoon,remove cooked chicken and vegetables from slow cooker and set aside.
6. Strain cooking liquid into saucepan.Skim off fat.Bring to a boil over high heat,stirring constantly.
7. In a small bowl,combine remaining 1 teaspoon Dijon mustard,,heavy cream and cornstarch.Whisk well.Stir creamy mixture into boiling liquid.
8. Cook for about 3 minutes or until mixture thickened.Stir in fresh tarragon.
9. Pour over cooked chicken.Serve immediately.