Sprinkle 1 tsp salt to dehydrate the chopped cabbage and allow to sit for 15 minutes. Squeeze the water from cabbage using clean tea towel then transfer to another bowl.
Cut scallions and mushrooms into small pieces then combine with cabbage and ground pork. Add garlic, ginger, sesame oil, soy sauce, salt, red wine vinegar and black pepper. Mix well with spatula then knead by hand until all combined. Cover and refrigerate for 30 minutes.
Add flour to a bowl and gradually add salted water then sesame oil and mix. Form dough into a ball - it should pick up all the flour off edges of the bowl. Knead the dough for ten minutes then cut dough in half. Roll each half into logs and wrap tightly with cling film. Allow to rest for 30 minutes.
Sprinkle cornflour on work surface and cut each log into 12 pieces. Form each piece into ball shape and use rolling pin to flatten centre of wrapper as you rotate it. Use ramekin or cup to cut wrapper. Stack completed wrappers under wet towel.
Take a wrapper and place it in the palm of your non-dominant hand. Use roughly a teaspoon of the mixture in centre of each wrapper. I filled about six at a time. Then dip finger into cold water and run 1/4” circle all around the outside edge of an individual wrapper.
Fold the wrapper in half over the filling and pinch it in the centre with your fingers. Working from centre out, use thumb and index finger to make 3-4 pleats on each side. Ensure you press the folded pleat tightly against the back part of the wrapper to minimise wrapper thickness and to ensure that there are no openings. Put each completed gyoza on a lightly floured baking tray and cover with wet towel until cooking.
To cook, heat the vegetable oil in a large non-stick frying pan over medium high heat. When the pan is hot, place the gyoza in clockwise, flat side down around the pan just ensuring they are not touching each other. Cook until bottom of ALL gyozas are golden brown (1-3mins) then add water (and cornflour) and immediately cover with lid and steam for about 3 minutes or until most of water evaporates. Add 1 tbsp sesame oil around the pan and cook uncovered until bottom of ALL gyozas are crisp.
Transfer to a plate with dipping sauce. For the dipping sauce, combine soy sauce and red wine vinegar in a small bowl and add freshly chopped ginger. Mix together and enjoy.
To freeze gyozas, lay them on baking tray without overlapping and allow to freeze for 1-2 hours. Then transfer to a freezer bag and store for 3-4 weeks.
