Add the flour, salt, and butter in a food processor and pulse until you have an oatmeal-like consistency. Remove the blade from the processor.
In another bowl beat egg, vinegar, and water until fluffy and pour into flour and mix to combine. Roll out about 8 inches of wax paper onto a clean, hard surface. Place the dough onto the paper.
Knead the dough into a ball, but be careful not to overwork it. Wrap the ball in wax paper and chill in your refrigerator overnight. You may also freeze the dough for at least an hour, or up to a week. Be sure to let the dough stand at room temperature for 20 minutes or so, if frozen, so that you can work with it when you're ready to make your shell.
When your dough is ready, flour your clean flat surface, and roll it out with a rolling pin. You want about 1/4 inch thickness, and you want to be sure it's large enough to fill your 9-inch pie pan. When your dough is ready, get your pan in place next to you, roll the dough onto your pin and raise it over your pan so that you can roll the flat dough over and into the pan without tearing it.
Take a knife to cut the excess dough off from around the pan. You want about an inch or so of extra dough to be able to crimp into the perfect crust. Save the leftover scraps. With your fingers, go around the pan gathering the extra dough to fold and pinch into little peaks. If you have a hot kitchen, you can put your pie shell into the refrigerator while you make the filling.