These open-faced dumplings are a staple of Hong Kong dim sum. Round gyoza skins work best here. If you can't find them, cut square wonton wrappers into circles using a three-inch biscuit cutter. Lining the bamboo steamer with cabbage leaves ensures the dumplings won't stick. To vary the texture and taste, top each dumpling with lump crabmeat or a small piece of scallop instead of shrimp, and dot with hoisin sauce instead of hot sauce.