Combine the spinach and water in a blender and blend till smooth. You can add a little extra water to make it easier to blend, if needed. An immersion blender will also work. Measure and set aside 2 fl oz of this for the dumpling dough. Leftover can be used for smoothies.
Potsticker / Dumpling Dough
In a bowl, mix the flour and salt together.
Create a well in the middle (like you would when making pasta), and add the spinach puree and half of the hot water slowly, while mixing with a wooden spoon until clumpy bits are formed. Add the rest of the water as needed. You can alternate mixing and pouring water, if that is easier.
Knead the dough clumps by hand to form one soft dough ball. If the mix is too dry, add a little more water (a little at a time or dip your hands in water and knead the dough with wet hands). If the mix is too sticky, add a little flour (a little at a time).
You should have a dough that is soft, not sticky, and firm enough to hold its shape.
Knead the dough further on the work bench for about 2 minutes. Use flour sparingly if the dough is getting sticky. The dough will look smooth at this stage and be a little stretchy/elastic.
You can let the dough rest like this in one big ball, or cut it roughly into four equal parts and knead each piece to form a dough ball.
Wrap the dough/dough balls tightly in plastic wrap (individually) or place it inside a ziploc bag and seal it (push out as much air as possible) and let it rest for 1 - 2 hours at room temp. You can use the dough immediately after it has been rested.
If you're using it the next day instead, place the dough in the fridge (sealed in storage bags) and return it back to room temperature before handling them.
Lightly dust your work bench and roll out each piece of dough into a 1 inch diameter log. Then cut it into 1 - 1.5 cm discs.
Roll out each disc (dusting lightly with flour as needed) to form a circle (about 3-4 inches in diameter). You can use a circle cutter to cut out the wrapper neatly if you prefer.
Fill and seal the dumplings/potstickers before moving onto the next portion of the dough.
Notes
Note 1 - Boil the water first, and then measure the required amount of water. Do not measure water first and then boil it, as evaporation = less water.Note 2 - If you're stacking the wrappers after cutting them out, they will require a little flour between each one to prevent them from sticking to each other. However if you do this, you might get a little bit of flour sticking to the wrapper which is okay, but not ideal. The best way is to keep the wrappers separately or place a cotton sheet between wrappers.