Place flour and salt in a medium bowl and whisk together.
Add diced butter and use pastry blender or forks to work until butter chunks are pea sized, but no smaller.
Drizzle vinegar and 4 Tbsp. water into mixture. Work liquid through mixture with your hands. Add 1 Tbsp. at a time, until mixture no longer feels dry and can be gathered into a ball.
Create two equal-sized balls. Flatten each into a disc, and wrap in plastic. If making a top, place both in fridge. Otherwise, place one in fridge for one hour and the other in the freezer to be used for another pie.
Preheat oven to 375°F.
Place dough on a lightly-floured surface. Roll out into 12" round, turning the dough one-quarter every few rolls.
Drape pastry over rolling pin and place in 9" pie pan. Press gently onto the sides and crimp top.
Place a piece of parchment inside, fill with pie weights, beans, or rice.
Brush outside with beaten egg.
Bake for 10 minutes. Remove from oven and set on cooling rack while you make the filling.