Combine all dough ingredients in a large mixing bowl. If using a mixer, use the paddle attachment and mix on low speed for one minute. If mixing by hand, use a large wooden spoon and mix for one minute. The dough should form a firm ball and shouldn't be sticky. Mix in extra flour or milk as needed to adjust texture.
Transfer dough to a lightly floured surface and knead for 30 seconds to make sure all ingredients are evenly incorporated. The dough should be slightly tacky but not sticky.
Preheat the oven to 400 degrees Fahrenheit, or 350 degrees Fahrenheit for a convection oven. Line 2 baking pans with parchment paper or silicone baking mats. Do not oil the paper or silicone mats.
Use a rolling pin to roll out the dough on a floured work surface, frequently lifting the dough with a metal pastry scraper or bowl scraper to be sure it isn't sticking and dusting with more flour underneath if need be. You can flip the dough over and continue rolling with the bottom side up. The goal is to roll it to about 1/8 inch thickness. Use a fork or dough docker and poke holes all over the surface of the dough. Brush the surface of the dough with an even coating of the egg wash and sprinkle with fine salt.
Use a small cookie cutter dipped in flour to make round crackers or cut into squares or diamonds with a pizza cutter. Place the crackers about 1/2 inch apart on the prepared pans. Gather any scrap dough and repeat the rolling out, egg wash and salting process until all dough is formed into crackers.
If making more than one pan of crackers you can bake them all at once. Place the pans on different shelves and bake for 8 minutes, rotate the pans and bake for an additional 8 to 12 minutes, or until the crackers are firm and lightly golden. Remove the pans from the oven and brush the hot crackers with the melted butter. Immediately, turn off the oven, then return the pans to the hot oven for 3 to 5 minutes. Remove the pans from the oven and let the crackers cool on the pan. The crackers are done when they have a rich golden brown color and are fairly dry and crisp. If they don't snap cleanly after they cool, return the pan to a hot oven for a few more minutes until they dry sufficiently to snap when broken.