Cut chicken into big pieces. Mix the barbecue sauce ingredients in a bowl. Marinate chicken in sauce for 2 hours or more.
Boil chicken in marinade for 10 minutes. Drain.
Bake in preheated oven (300 °F) until brown, occasionally brushing with melted butter and barbecue sauce.
Thicken sauce with a little cornstarch (dissolved in water). When serving, top baked chicken with this sauce. Garnish with spring onion or parsley.