This starts by making a simple, flavoring marinade for the pork. So, in a good size mixing bowl, thoroughly stir together the mushroom-flavored dark soy sauce, and the chopped mushrooms. Then mix in the ground pork, Chinese five spice powder, and Shaoxing rice wine.
Once that mixture is well combined, it’s time to give the filling some hot-and-fast stir frying. For this, I used a deep-sided, heavy-bottomed, 12-inch skillet.
Heat the sunflower oil in the skillet over a high heat. As soon as it starts shimmering — but not quite smoking — quickly stir in all the pork mixture. Keep the heat on high, and use a sturdy spatula to stir-fry the mix for 2 minutes. Keep stirring all the time, using the spatula to break the mix apart into an even consistency as it fries. Good.
Now add all the remaining ingredients for the filling — the chilies, cabbage, and sesame seeds — and keep stir-frying for another 2 minutes. Remove from the heat, and stir in the bean sprouts. That’s it, the pork filling’s done.
Turn the whole lot into a big colander set over a good size bowl, and leave it aside to drain and cool while you make the filling for the vegetable spring rolls. Do not discard the marinade / cooking liquid that drains from the pork filling — it’s going to be the base for your full-bodied, dark dipping sauce.