Once dough has doubled in size, knock the air out and roll it into a cylinder. Cut into equal pieces, each approximately 60g (2oz). (This recipe makes 4. If you doubled or tripled the recipe, divide into 8 or 12 respectively.)
Shape each piece into a round disc shape, cover with cling film (or clean damp cloth) and rest for 15 mins.
Take the filling out of the fridge and divide it into approximately 60g (2oz) portions for each wrapper. Place each ball of dough on a chopping board and flatten it with your palm. Then, use a rolling pin to thin out the edges. The centre should be about 5mm (1/4 inch) thick and the edges should be about 2mm thick.
Roll a portion of the filling and place it in the centre of the dough. Bring the top and bottom edges to the middle and pinch them together. Repeat with the left and right edges, then each pair of parallel corners. (See in post for pictures of how to do this.) Finally, pinch the middle and twist to firmly close the nikuman.
Place each completed nikuman on an individual square of baking paper, then place them in the steaming basket. Be sure to leave plenty of space between each nikuman and the edges of basket.
Add the lid on and rest for 15 minutes for the 2nd rise.
After 15 minutes, fill the steamer with cold water and place the steaming basket with the nikuman on top. Place it on the stove and bring to a boil over a high heat. Once it starts to boil, set a timer for 13 minutes.
Remove the lid and enjoy!