In a large stockpot, add 4 quarts salted water to cover the chicken and bring to a boil.
Add the ginger and chicken and let the water come to a second boil. Turn of the heat but leave the pot on the stove. Cover pot and let the chicken sit in the hot water for 30 minutes. Drain the chicken and set aside to cool. When it is cool enough to handle, split the chicken in half. Pat very dry and place in a large mixing bowl.
Combine the five-spice powder, sugar, and salt in a small bowl. Working with a sprinkle at a time, rub the spice mixture onto the chicken skin. Continue until all the spice is used. Refrigerate the chicken, uncovered, overnight.
An hour before serving, take the chicken out of the refrigerator and let sit at room temperature. In a wok or deep large saucepan, heat enough oil to almost cover the chicken, about 3 to 4 cups. Bring oil temperature to 325 to 350 degrees. (Chicken should sizzle upon contact with oil.) Fry the chicken until nicely brown and crisp, 3 to 5 minutes on each side. (Depending on the size of your pan, you may have to fry the chicken in separate batches. Cover pan with a screen if oil begins to splatter. Remove chicken and drain on paper towels. Cut each chicken half into 2 to 3 pieces and place on a large platter lined with watercress. Serve with ginger-lime dipping sauce.
source from: vietnameseportal