Finely dice 150 g thinly sliced pork belly using a knife.
Place the diced pork belly in a mixing bowl with 150 g ground pork, ½ tsp Japanese soy sauce (koikuchi shoyu), ½ tsp oyster sauce, 1 tsp sake, 1 tsp toasted sesame oil, ½ tbsp sugar, ½ tsp salt and 1 pinch ground black pepper. Knead together by hand until evenly distributed.
In a separate bowl mix 30 g Japanese leek (naganegi) and 60 g canned bamboo shoots with 2 tbsp potato starch (katakuriko) until evenly coated.
Combine the two bowls into one and add the ¼ onion and 5 g grated ginger root. Knead together until the ingredients are evenly distributed through the filling.
Start boiling a pot of water and line the steaming basket with a sheet of baking paper.
Take a wonton wrapper and place it in the palm of your hand. Add about 1 tbsp of the filling to the centre (approx 15g per shumai) leaving space around the edge.
Make a circle with your thumb and fingers and use a cutlery knife to push the shumai down into the circle, this will push the edges of the wrapper up and keep the dumpling round. You can also flatten the base by pushing it up slightly from underneath.
Use the knife to smooth out the top and place it on top of the baking paper in the steaming basket. (See the post above for more process pictures.)
Repeat until you've used up all the wrappers and filling, then place one green pea in the center of each shumai.
Once your pot of water reaches a rolling boil, place the steaming basket on top with the lid.
Steam the shumai for 8 minutes.
Serve with Japanese mustard (karashi) and Japanese soy sauce (koikuchi shoyu).
Enjoy!
Notes
Steam before storing. Once cooked, refrigerate and eat within 1-2 days. To freeze, place the cooked shumai on a tray with a little space between to stop them from sticking together. After 2-3 hours, transfer to a ziplock bag or airtight container and eat within 2 weeks.Steam again or microwave until piping hot to reheat.