Preheat oven to gas 6, 200°C, fan 180°C.
Season the chicken inside and out with salt and pepper.
Put 3 sprigs of tarragon inside the chicken cavity.
Squeeze the lemon juice over chicken and put the squeezed half inside the cavity. Smear the chicken with butter.
Cook in the preheated oven for 15 minutes, then lower temperature to gas 4, 180°C, 160°C fan and cook for another 1 hour. Check the chicken is cooked through by inserting a sharp knife into the thickest part of the thigh - the juices should run clear.
Remove from oven, cover with foil and leave to rest in a warm place. Pour the fat and juices from the roasting tin into a small saucepan.
Deglaze the roasting pan by adding the Noilly Prat or wine to it, placing it over a moderate heat and scraping up all the sticky residue with a wooden spoon.
Add this to the pan of juices and boil until reduced to no more than 1 or 2 tablespoons. Add the stock and a sprig of tarragon. Bring to the boil again and boil until reduced by one-third. Stir in the creme fraiche and boil until reduced to a light coating consistency. Chop the remaining tarragon and add that with any juices that have come from the resting chicken.
Serve the carved chicken with the tarragon cream sauce.
*Inspired by Lucinda B. featured in the Realfood Cookbook
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