Roughly chop the spring onion and add to the Thermomix bowl. Cut the ginger into quarters and add to the Thermomix bowl. Chop for 5 seconds / speed 5. Scrape down the bowl and repeat 5 seconds / speed 5.
Add the pork, sesame oil, salt, soy sauce, vegetable oil and egg. Mix for 10 seconds / speed 3 and then use the Dough function / 1 minute.
Transfer the mixture to a bowl and set aside in the fridge to marinade for 1-2 hours.
30 minutes before you are ready to make the dumplings, cut the cabbage into large pieces and add half (250g) to the Thermomix bowl with half a teaspoon of salt. Chop for 10 seconds / speed 4.
Transfer the chopped cabbage to the simmering basket and set aside to drain for 30 minutes. (Place the simmering basket over a bowl or in the sink as liquid will seep out of the cabbage).
Repeat with the remaining 250g cabbage and ½ teaspoon of salt. Chop for 10 seconds / speed 4 then add to the simmering basket with the rest of the cabbage.
After 30 minutes is up, squeeze out any excess water from the cabbage.
Return the pork mixture and the cabbage to the bowl and mix for 5 seconds / REVERSE / speed 5.