Soak the mushrooms in hot water until soft, 20 to 30 minutes. Rinse with tap water and gently rub to remove any dust. Drain and squeeze excess water. Mince into small pieces.
Combine the rest of the filling ingredients. Stir to mix well, until the paste becomes sticky and a bit springy.
Work on the shumai one by one. Place a dumpling wrapper on a clean work surface. Place 1 tablespoon of filling in the center of the wrapper. Bring the edges up around the filling, pinching and pleating, leaving the top open. Repeat with the remaining wrappers.
Line your steamer with a clean, wet dish towel or steaming parchment (*footnote). Transfer the shumai into the steamer, one finger’s width apart. Cover and steam over boiling water for 8 minutes, until cooked through.
Serve with dumpling dipping sauce of your choice or Chinkiang vinegar.
Store and cook frozen
Place the uncooked shumai on a lightly greased baking sheet, one finger’s width apart. Cover the sheet with plastic wrap. Freeze the shumai until completely frozen. Then you can transfer them to bags or containers to save freezer space.
Steam the frozen shumai without defrosting or thawing. After bringing the water to a boil, steam until completely cooked through, 15 minutes or so.