Place chicken under a heated broiler and brown on both sides, about 10 minutes. Place green onions, ginger, garlic, chicken stock, soy sauce, and pepper in large pot. Bring to boil, reduceheat to simmer, and cook 4 to 5 minutes.
Add browned chicken. Cover and simmer 25 minutes. Turn occasionally. Add sherry and sugar. Simmer another 25 minutes, tightly covered. Add a little water if liquids dry out during cooking.