Chicken with tarragon sauce

1) Preheat oven to 200°C, Gas 6
2) Joint the chicken or ask your butcher to do it. Rub the skin of the chicken all over with the lemon half.
3) Put the chicken in a roasting tin with the lemon and 3 branches of the tarragon.Smear the chicken thickly with butter. Season generously and roast for 40 minutes until cooked through.
4) Transfer chicken to a serving dish and cover with foil to keep warm.
5) Remove the lemon and tarragon stalks and skim off as much fat as possible from the roasting tin, leaving the juices.
6) Place the tin on the hob. Pour in the vermouth. Bring up to the boil, scraping the roasting residues, and reduce to a few spoonfuls. Stir in the cream and reduce to a good consistency. Season to taste with salt, pepper and lemon juice.
7) Serve with the chicken and top with the remaining tarragon leaves.