Add shumai mixture, excluding onion and cornflour, to the bowl. Mix well until the mixture becomes almost like a paste.
Then add onion and cornflour and mix well. Cover and leave for 1-2 hours in the fridge.
Sprinkle small amount of cornflour (not in ingredients) over the tray where the shumai will be placed as you make them.
1. I used the Japanese shumai sheets which comes in a pack of 24 sheets. The size of the sheet is 6.5cm (2½") square. You could substitute it with the Chinese shumai or wonton sheets which are usually 9cm (3½") square. If the size of the sheet is larger, you will need more meat to fill up the sheet or reduce the number of sheets to make.
2. To use up the meat perfectly, I draw 4 lines on the surface of the meat crossing in the centre so that it will make 8 pieces like pizza. Then roughly divide each piece into 3 equal portions. This will make 24 lots of meat.
3. For more details on how to steam without a steamer, please visit Sakamushi Fish (Steamed Fish in Sake). You will even find out how to take the steamed hot plate out of the pot without burning your fingers.
4. It is unlikely that the shumai skin at the bottom will stick to the plate but I thought it would be pretty to have a paper liner anyway.
5. You can freeze before or after steaming them. When freezing, place each shumai without touching each other. Once frozen, you can pack them closely.
Frozen shumai can be steamed without thawing. It will take 10-12 minutes.