Put the roughly chopped cabbage in a food processor and process until finely chopped.
Remove the cabbage to a large bowl and sprinkle with salt. Allow to rest for 10 minutes. Doing this drains the moisture from the cabbage and ultimately the filling, to prevent soggy dumplings.
In the meantime, return the food processor to the stand and add the ginger, spring onion, ground pepper, soy sauce, rice wine vinegar and egg.
Pulse to mix the ingredients well. Remove from the blender and set aside.
After 10 minutes, squeeze excess liquid out of the cabbage. Place the cabbage in a cheesecloth or paper towel and squeeze tightly to remove excess liquid.
Place the dry cabbage back into the large bowl, add the chicken and seasoning mixture. Mix well.
Mix together the slurry (1 tablespoon cornstarch + 1/2 cup water).
Take one dumpling wrapper, spoon about 1 tablespoon of the pork mixture onto the middle of the wrapper. Dip one finger into the slurry and “paint” the edges of the dumpling wrapper. Bring up the bottom side of the wrapper, fold up and press to shape into a half-moon shape, encasing all of the filling.
Place on baking sheet, cover loosely with plastic wrap and repeat with rest of dumplings. Make sure that the dumplings do not touch each other on the sheet.
When all dumplings are assembled, lightly spray them with cooking oil to prevent them sticking to each other when cooking.
To pan fry:
Add a little oil to the pan and preheat.
Place several dumplings in the pan close but not touching each other.
Add about 1 tbsp of water and cover with a lid.
Cook for about 10 minutes checking to make sure that the bottom of the dumpling does not burn.
Once cooked, remove and repeat for the remaining dumplings.