Start by preparing the filling - finely dice the mushrooms, cabbage, spring onions, ginger and garlic. See my notes for saving time by using the food processor.
Heat a little oil in a large frying pan - add the mushrooms and cook for about 5 minutes until they’ve reduced and released lots of moisture.
Add the cabbage, garlic, ginger and white pepper, cook for a further 5 minutes until the cabbage has softened.
Taste the filling and add salt or soy sauce to taste. Set to one side to cool slightly before continuing.
Fill the gyoza
Put some cold water in a small bowl. Lay out 4 - 6 gyoza wrappers in front of you to create a production line. Don't work with more than this at a time as the wrappers can dry out quickly. If you find the gyoza are sticking as you work, you can very lightly dust your counter with cornflour.
With clean dry hands cup a filled wrapper in one palm, fold over and press in the middle. Now pull one side of the wrapper in to the middle, then the other to create two little tucks either side of the centre. A couple more tucks will seal the gyoza. This action will automatically form a curved shape, since the wrapper is being shortened on one side.
Place on a baking sheet lightly dusted with cornflour and repeat until all the filling or wrappers are used up. (leftover filling can be frozen).
Cook the mushroom gyoza
Heat a little oil in the non-stick pan. Place the gyoza into the pan flattest side down, either in rows or fanned out from the centre.
Cook for 3-4 minutes until golden on the base. Gently shake the pan from time to time to stop them sticking too much.
The second stage of cooking gyoza is steaming. Have the lid ready to put on, pour in about 2 tbsp water into the pan and quickly put the lid on - it will spit.
Steam for 3-5 minutes until most of the water has evaporated and the wrappers are tender on top.
Serve as you wish or sprinkle with toasted sesame seeds, sliced spring onion and your favourite dipping sauce.
Notes
To use the food processor - process the mushrooms first, pulsing them for a couple of seconds to give a fine dice, then throw them into the pan. While the mushrooms sweating, put the cabbage, spring onions, ginger and garlic in the food processor and pulse again to a fine dice.To make a spicy dip - mix 2 tablespoon rice wine vinegar, 1 tsp sesame oil, 1 tsp mirin, ½ tsp chilli flakes. Or substitute chilli oil instead of the sesame oil and chilli flakes.