This is from ” Modern British Food” by Sybil Kapoor.
Preheat the oven to 230 C, 210 Fan, Gas 8. Squeeze some of the lemon over the chicken and put the halves into its cavity with the rosemary or tarragon.
Rub the chicken with olive oil and season well. Place in a roasting tray. Dot the butter on to the chicken breasts.
Roast for 15 minutes then reduce heat to 190 C, 170 Fan, Gas 5 and cook for 35 minutes more.
Check that the chicken is cooked by inserting a skewer between the thigh and breast. The juices should run clear.
Remove from the oven and leave to rest while you make a gravy with the juices.