Season the chicken breasts with salt and pepper and coat them lightly in flour.
Brown the chicken in the butter for 4 to 5 minutes on each side and then transfer to a plate and cover with foil to keep warm.
Add the Riesling wine and chicken stock to the same skillet you cooked the chicken in.
Bring the sauce to a boil.
Cook for a few minutes until the sauce reduces down a bit
Add the heavy cream and continue to cook the sauce for a few more minutes.
Stir in grapes and tarragon.
Return the chicken to the skillet with any juices that have accumulated on the plate and heat for another few minutes until chicken is cooked and heated through.