Place flour into whatever mixer you are using and sprinkle the salt on top. Whisk these together.
Cube the chilled butter and drop into flour mixture. combine until it appears like rough sand (it's okay to leave larger chunks of butter, in fact this will help with the flaky texture)
Drop the egg onto the top of the flour mixture, then add 1 tablespoon of cold water, and work in well. Dough should come together like play dough. Use your hands and create a dough ball (I do a kneading motion a couple times to bring it all together), roll this in plastic wrap, place in the fridge for an hour.
Once the dough is chilled, flour your work surface, and roll out to cover a pie tin completely. Use lots of flour to avoid tears! Fold crust in half and place it into the pie tine. Lifting and pressing the crust into the bottom of the tin, trim the overlap dough and crimp as desired.
Notes
Dough can be made ahead and placed in fridge overnight.
You can substitute margarine for the butter, but you'll notice a quality difference. Butter is just a top choice for dessert crusts.
Some recipes will want you to 'blind' bake or pre-bake your crust. Preheat oven to 400º, if using pie weights (for even crust) use parchment paper! Bake crust for 15-20m till tan.