Soak the dried mushrooms in cold water for at least 5 hours or overnight. Rinse mushrooms under running water. Drain. Add 1 tablespoon corn starch. Rub the mushrooms all over with the starch to remove dirt. Rinse. Remove the stems with scissors. Squeeze out as much water as possible. Pat dry with paper towels. Cut into ¼-inch dices. Set aside.
Wash the spinach thoroughly for at least 2 times to remove all the sand and dirt. Drain. If there are roots, cut to remove.
For the pork, cut into thin strips. Then, cut the strips into tiny dices. Gather the meat together, pat down slightly. Chop repeatedly and rapidly, fold and chop again. Repeat the same motions until the meat turns into ground meat. Transfer to a medium bowl. Stir for a few times until the meat is slightly sticky. Add marinade and mix well. Add the mushroom and mix again. Divide into 12 (1½-inch) portions. Roll into meatballs and squeeze tight slightly.
In a large pot over high heat, add 8 cups water. Bring to a boil. Once boiling, add spinach and cook the stems are just softened, about 2 – 3 minutes. Remove the spinach to a large bowl. Add the meatballs and cook until they float, about 3 – 4 minutes. Season with salt to your own taste. Return the spinach to pot and cook for 1 more minute. Turn off the heat. Transfer to serving bowls. Serve immediately.