Weigh flour in a bowl and slowly add water, gently stirring until light clumps have formed. Finish by kneading with your hand until fully combined then cover and rest for 10 min.
After resting knead the dough into a smooth ball then cover again and rest for an additional 30-60 min.
Chop cabbage into small pieces. Transfer to a colander in the sink and add salt. Massage entirely and let it sweat for 10-20 min before squeezing out any leftover moisture.
Chop the mushrooms into small pieces then dry cook them in a pan on medium heat for 5-6 min to release moisture.
Transfer the cabbage and mushrooms to a mixing bowl then add the remaining filling ingredients, stirring to combine well.
Divide the dough into 4 sections. Roll each section into a rope then cut into 5-6 equal pieces.
Flatten a section of dough in the palm of your hand then use a small rolling pin to roll out each side evenly. Flip and repeat until the wrapper is a thin disc.
Place the wrapper in your hand and add a small scoop of the filling in the middle. Add warm water to the edges and squeeze edges together until tightly sealed.
Place the dumpling on a cookie sheet lined with parchment paper dusted with flour. Continue making dumplings until all the dough is gone.
Bring a large pot of salted water to a boil. Add 15-20 dumplings and cook for 6-8 minutes.
Use a slotted spoon to remove and serve with desired dipping sauce (e.g. soy sauce, chili oil, etc).