1. Wipe chicken with a damp cloth. Mince ginger root; then combine with soy sauce, sherry, salt and pepper. Rub mixture over chicken inside and out. Let stand 1 hour.
2. Cut scallion stalk in 1/2 inch sections. Slice and crush remaining ginger root.
3. Heat oil. Add scallion and ginger root; stir-fry a few times. Add remaining soy sauce and bring to a boil. Cook 2 minutes over medium heat.
4. Hold chicken upside down over a bowl. Pour heated soy mixture into its cavity, letting it drain out through the neck into the bowl. Repeat 5 times, reheating sauce after the second and fourth time.
5. Transfer sauce to a large pan and slowly bring to a boil. Add chicken and cook, turning, until evenly colored (about 10 minutes).
6. Boil water and add to chicken and sauce. Simmer, covered, 10 to 15 minutes. Add sugar and simmer, covered, 2 minutes more.