Note 1: Dumpling pastry wrappers are available at my local supermarket in the chilled section. If yours doesn’t stock them you should be able to find them at any gourmet or Asian supermarket. Alternatively, you can use square wonton wrappers and fold into a triangle shape, if these are available to you.
Note 2: You can substitute with white wine vinegar if you don’t have any rice wine vinegar.
Note 3: The dumplings do not refrigerate well overnight as they will go soggy. Therefore, I recommend you make these on the day you wish to serve them. Alternatively, they freeze very well. To freeze, place dumplings in a single layer and not touching on a baking sheet lined with baking (parchment paper). Place in the freezer for a few hours then remove and transfer into a zip lock bag.