1) First, make the sauce, which can be done a day in advance of the final preparation. Combine all of the sauce ingredients in a non-metallic bowl and mix well. It does not matter in which order the ingredients are combined. Cover and refrigerate until time to use.
2) Next, make the filling. Combine all of the ingredients in a non-metallic bowl and mix very well using your hands. Again, it does not matter in which order the filling ingredients are added. Once the filling is made, set it aside.
3) Now it's time to fill the dumplings. Line a large baking sheet with parchment paper and dust the paper heavily with the cornflour. Take a gyoza wrapper and put a generous teaspoon, almost 1 tablespoon, dollop of filling in the middle of the gyoza wrapper. Now start pinching in the wrapper all the way around the dumpling to close it up, like a fold/pleat; approximately 4 folds. Then give it a little twist around the dumpling's waist. Arrange the finished dumplings on the cornflour coated baking sheet. When all 40 dumplings are finished, cover and refrigerate for half an hour.
4) Add the rapeseed oil to a large 30 cm non-stick skillet. Start adding the dumplings to the pan and turn the heat to medium-high. Brown the bottom of the dumplings, about 2 minutes. Reduce the heat to medium, add the sauce, cover the pan and steam for 2 minutes. After 2 minutes, uncover the pan and turn over all of the dumplings to coat with the sauce.
Transfer to a serving dish and enjoy.
A viewer, who may not be a professional cook, provided this recipe. The Food Network Kitchens chefs have not tested this recipe and, therefore, we cannot make representation as to the results.