Combine the pork, water chestnuts, soy sauce, vinegar, oil, sugar, ginger, cornstarch, salt and pepper in a bowl and mix well to combine (hands work well for this). Place a dumpling wrapper in the palm of one hand and cup it loosely. Place a generous tablespoon of filling in the center of the wrapper. With your free hand, gather the sides of the wrapper around the filling, letting the wrapper pleat naturally. Squeeze the middle gently and tap the dumpling to flatten the bottom so that it can stand upright. The meat filling will show a little at the top. Make the remaining dumplings in the same manner.
Arrange filled dumplings about 1/4 inch apart in two steamer trays that have been lined with wet cheesecloth. (At this point, you can refrigerate dumplings, covered, for 24 hours.)
When ready to steam, fill a wok or lower part of a steamer with water so that it comes within an inch of the steamer tray, and bring to a rolling boil. Stack the steamer trays in the wok or steamer, cover tightly, and steam dumplings for 20-25 minutes over high heat, reversing the trays after 10 minutes. Use a slotted spoon to transfer dumplings to a platter and serve with Spicy Dipping Sauce.
SPICY DIPPING SAUCE:
Combine ingredients in a small bowl and serve with Pork Dumplings.