1. Place chicken, wine, onion, stock, bay leaves, salt and pepper in a sauce pan, and bring to a boil. Reduce heat, cover and boil gently for about 10 minutes. Transfer the meat to a dish and keep warm.
2. Measure the cooking liquid. There should be about one cup; if there is more, then reduce to one cup. Stir in the dissolved potato starch, bring to a boil, then add half and half and bring to boil. Return chicken pieces to pan, add the tarragon and thyme and heat through. Remove from heat and slice into diagonal strips. Garnish with a tarragon sprig and serve.