You’ll be surprised by how moist this chicken cooks up; it’s a great technique to use for any number of other chicken dishes. This dish has a bit of kick, so temper the garlic, ginger, and chilis if you’re sensitive.
Fill a large soup pot with 6 quarts water. Add chicken and bring to a boil. Boil 10 minutes. Turn chicken and cook another 10 minutes. Turn off heat and cover tightly. Let sit 2 hours.
Remove chicken; it’ll be chopstick tender. Discard skin and bones.
Arrange watercress on a large serving platter. Shred meat and place meat on top of watercress.
In a wok or large sauté pan over high heat, heat peanut oil and add chili pepper, ginger, garlic, scallions, peppercorns, soy sauce, sherry, cornstarch paste, and sesame oil. Stir and cook 2 minutes.
Pour sauce over chicken and serve.