To make the sichuan oil, place all ingredients in a small saucepan and place over very low heat to infuse – approximately 30 minutes to 1 hour (do not let the oil boil) – then set aside to cool. This oil can be refrigerated and kept for about a month, the flavour continuing to develop.
Place pork mince in a bowl and add the prawns, mushrooms, ginger, garlic, chives, soy, sesame oil and chilli oil and use your hands to mix thoroughly. You can do this in a food processor, but make sure not to over-mix – it is nice getting a pop of prawn when biting into a dumpling, and too much processing can also make the pork’s texture too paste-like.
Lay out four wrappers at a time on your bench. Place a heaped teaspoon of filling mixture in the centre of a wrapper, dab a little water around the edges, then fold lightly over to make a semicircle, pressing firmly just around the filling to make sure no air will be trapped inside. Pleat the upper edge with a series of pinches as you seal the dumpling. (You can also cheat by using a fork to make small indents on the curved edge). Place aside in a single layer on a paper-lined tray. Continue until all the mixture has been used.
Place a single layer of dumplings in a bamboo steamer lined with steamer paper (available from most Asian groceries, otherwise use baking paper with small holes punctured into it to let steam through). Place over a large saucepan of boiling water, making sure the steamer fits snugly on the pot, so as not to let steam escape. Steam for about 10 minutes or until the wrappers are tender and the filling is cooked. Transfer to a plate.
Drizzle dumplings with a little black vinegar and serve alongside the Sichuan oil.