Put oxtail pieces in large pot; add 1 cup of water. Sprinkle with salt, pepper, and ground ginger. Bring to a boil, lower heat, and simmer for 30 minutes. Add remaining 8 cups of water, peanuts, and fresh ginger. Simmer for 1 1/2 more hours; skim off excess fat. Remove stems from mushrooms, dice caps. Stir mushrooms, onion, and optional chili pepper flakes into soup. Cook about 1 to 1 1/2 hours more, or until meat is tender. Garnish with kai choy, green onions, and Chinese parsley. Makes 6 servings.
