For the filling:
3 tablespoons oil, plus ¼ cup
1 tablespoon minced ginger
1 large onion, chopped
2 cups shiitake mushrooms, chopped
1 1/2 cups cabbage, finely shredded
1 1/2 cups carrot, finely shredded
1 cup garlic chives (Chinese chives), finely chopped
1/2 teaspoon white pepper
2 teaspoons sesame oil
3 tablespoons Shaoxing wine or dry sherry
2 tablespoon soy sauce
1 teaspoon sugar
salt, to taste