1.Wash chicken under cold water; pat dry inside and out with absorbent paper.
2.Combine garlic, ginger, sauce, sherry, pepper and oil in a large bowl; add chicken, coat in marinade. Cover; refrigerate overnight.
3.Preheat oven to 220°C/425°F.
4.Place chicken on an oiled wire rack in a large baking dish. Half-fill baking dish with water (it should not touch the chicken). Roast, uncovered, about 1 hour 20 minutes or until cooked through.
5.Meanwhile, make shantung sauce. Stir sugar and the water in a small saucepan over low heat until sugar dissolves. Bring to the boil; boil, uncovered, without stirring, about 5 minutes or until sauce thickens slightly. Remove from heat; stir in vinegar and chilli.
6.Remove chicken from oven; when cool enough to handle chop meat coarsely; discard bones. Serve drizzled with shantung sauce.
Sichuan peppercorns are a mildly hot spice native to the Sichuan province of China. While not related to the peppercorn family, the small, red-brown aromatic sichuan berries look like black peppercorns and have a distinctive peppery-lemon flavour and aroma.