Slice cold butter into pats.
Whisk salt and flour together.
Add butter in and using a pastry cutter mix it together until it forms a sablage, or looks really, really crumbly and there isn’t much flour left that hasn’t been incorporated into the crumbles.
Form a well in the sablage by digging your fist down in to the center, and then add in the egg and milk.
Mix the egg and milk in with the sablage until a dough forms.
Form the dough into a ball, and then pat the ball down so it is more of a disc. Wrap in plastic wrap and place in the refrigerator for at least an hour, and up to a day. When you bring it out of the refrigerator, give it a few minutes to soften so that you can roll it out, but don’t let it take too long, or come to room temperature, or the butter fat will start to melt.
Place the dough on a well floured surface and/or parchment paper. Roll the dough out to your desired thickness for a pie, quiche, or galette.
Either line a pie pan with it for a traditional pie or quiche, or place on parchment paper in the center of a baking sheet and fill with your desired toppings.
Brush the sides of the crust with the beaten egg/egg wash, so that the crust bakes to a warm golden brown color.
Bake at 350 degrees for approximately 25-30 minutes, or until the filling is done and the pie crust is golden brown.