Measure out one cup of flour and slowly add the hot water and salt liquid in a mixing bowl. Use a spoon or chopsticks to mix the flour with the water.
When the water is incorporated into the flour, you should have a slightly sticky ball of dough. If necessary add additional flour if it’s too wet (the dough is wet to the touch and not forming into a ball or releasing from the sides) or water if it's too dry.
On a floured surface, begin to knead the dough by hand for about five minutes. The end result should be a smooth and round ball of dough. Optionally, you can use a food processor to mix your dough and flour and run the food processor until the ball of dough forms. Knead the dough for three minutes by hand.
Leave the dough to cool to room temperature and then wrap it with cling wrap to rest for at least 30 minutes on the counter. The dough should be ready once you can press a finger on the dough and it leaves a small imprint.
Use your pasta machine to roll out the dough and stop at the thinnest setting or until you reach about 0.3 millimeters. One my Marcato Atlas machine, this is level 9.
Using a 80mm / 3 ¼ inch diameter circular cookie cutter, cut out wrappers from this dough. This should make about 50 dumpling wrappers.
If you want to stack the wrappers, lightly spread two pinches worth of cornstarch on the top of each wrapper and stack them one on top of the other to prevent sticking. You can freeze the wrappers in an airtight container to use for later.
Filling
Mince the shrimp and add it into a large mixing bowl with ground pork. Add the rest of the ingredients and mix thoroughly.
Test the seasoning of the meat by putting ¼ of a teaspoon size of meat in the microwave for ten seconds. Adjust the seasoning if necessary based on your preferences.
Assembly and steaming
Make a circle with your pointer finger and thumb. Place one wrapper on top and add about one tablespoon of filling.
Cover the sides of the filling with the wrapper and try to keep a cylindrical shape.
If you need to form the uncovered meat on the top of the shumai, dip your hand in the water and shape it. You should end up with cylindrical-shaped dumplings.
Optional: you can add minced carrots at the top for extra color.
Line your steamer with parchment paper or lettuce. Preheat the steamer before adding your shumai.
Add shumai in the steamer and cook for about ten minutes per batch. Test one of the shumai by removing it from the steamer and lightly pressing the top. Finished shumai should feel springy to the touch and the color on top should be a pale gray. Use a thermometer to check if the temperature has reached at least 165 °F.