Unless cooking whole, cut the chicken in half or into quarters using poultry shears or a sharp knife.
Place the shallots, garlic, herbs, salt and spices in a food processor or blender and process until the shallots are finely chopped. Add the butter and process to make a smooth paste.
Thoroughly rub the paste over the skin of the chicken and then allow it to stand for 1-2 hours.
Preheat the oven to 400°F (Gas 6/200°C) and place the chicken in a roasting tin. Quarter the lemon, if using, place one or two quarters around the chicken pieces (or in the body cavity if the chicken is whole) and squeeze a little juice over the skin.
Roast for 1 hour-1 hour 15 minutes (2 hours-2 hours 30 minutes for a whole bird) until the chicken is cooked through and the meat juices run clear. Baste occasionally with the juices in the roasting tin. If the skin browns too quickly, cover the chicken loosely with foil.
Allow the chicken to stand for 5-10 minutes, covered in foil, before carving, and then serve garnished with sprigs of fresh parsley or coriander.