Tip flour and salt into medium bowl, combine with whisk.
Heat water to 115℉ (use an instant-read thermometer to gauge temperature), add to dry ingredients. Using your hands, combine to form a rough dough. It might seem like there's not enough water at this point - rest assured there is.
Transfer dough to a clean surface (I use a large bamboo cutting board) and knead for about 5 minutes, incorporating any bits of flour left in the bowl. Dough should easily form into a ball, and be slightly tacky but not sticky.
Place dough ball into a quart-size plastic zipper bag, seal shut, and rest in the fridge for at least an hour. This rest time allows the gluten to develop and will result in a much easier-to-manage dough. Near the end of the rest time and when you are ready to assemble the dumplings, mix the filling.
With the dough rested and filling mixed, remove the dough from the fridge. Using your kitchen scale, measure your whole dough ball in grams and divide by 25 - this will give you an idea of how many dumplings you will be able to make. It should be about 19 dumplings.
Cut your dough ball into quarters, and seal all but one of them back in the baggie. Cut a small amount of dough from the remaining quarter with a bench scraper. You're looking for a uniform size/weight of 25g for all of your dumpling wrappers, but also you want to ensure you're going to get the full amount of wrappers from your dough. You might need to cut your chunk smaller, or add a bit more from your dough. This might seem difficult at first but with practice it gets easier very quickly. Try to keep all of your dough except your "working dough" sealed in the baggie.
Once you've got a 25g chunk of dough, roll it into a tight sphere, then flatten the sphere with the bottom of a pint glass. The glass I use in the video is a little shorter than a pint glass, but has the same footprint. I try to flatten the sphere to be exactly the diameter of the bottom of the glass.
Using a handheld rolling pin, take your dough circle and roll it out to a 4" diameter. Start from the center of the dough and roll the pin towards you, then rotate the dough circle so that is flattens evenly. It's helpful at the stage to have a 4" circle template to measure your wrappers. I use a fried egg form, but you can substitute with anything you have lying around (a small bowl, a container lid, etc).