Pat the turkey dry inside and out with kitchen paper. Rub the cut lemon halves lightly over the skin of the turkey. Season inside and out with salt and pepper to taste. Place the lemon halves, apple, onion, and potato into the cavity of the turkey. Place into a close-fitting roasting tin.
Stir the butter and honey together in a small saucepan over medium-low heat until the butter has melted and the mixture is evenly blended. Spoon the honey mixture over the turkey, coating the entire outer surface. Allow to stand 30 minutes, reapplying the honey mixture several times.
Preheat the oven to 200 C / Gas 6.
Bake the turkey in the preheated oven for 30 minutes, basting two or three times with the drippings and honey mixture. Reduce the temperature to 180 C / Gas 4, and cook 30 minutes more, basting frequently. If needed, add the chicken stock to keep the roasting tin dripping from drying out.
Cover the turkey with aluminium foil, and continue roasting until no longer pink at the bone and the juices run clear, 1 1/2 to 2 hours longer. A cooking thermometer inserted into the thickest part of the thigh, near the bone should read 82 degrees C. Remove the foil during the last 15 minutes and baste one last time. Remove the turkey from the oven, cover with a double sheet of aluminium foil, and allow to rest in a warm area for 15 minutes before carving and serving.
This recipe is for a small turkey, but it can be doubled or tripled easily for a larger bird. Just adjust the roasting time (15 to 20 minutes per 450g).