Stir together flour and salt, then add the fat using your fingers or a pastry cutter.
Cut the fat into the flour mixture until the largest pieces are pea-sized, but most of the mixture resembles coarse breadcrumbs.
Beat the lemon juice/vinegar with the egg and cold water, then sprinkle over the flour mixture, blending lightly with a fork. Be patient, using your hands only at the end to bring the dough together. It will be crumbly and that’s okay — chilling will help it come together.
Cover with plastic wrap and refrigerate at least an hour, or up to overnight.
When you’re ready to make the pie, preheat your oven to 425°.
Lightly flour your counter and roll the dough out into a circle large enough to fit your pie pan with a little overhang; gently lift the crust into your pan, crimping the edges to fit and patching any thin spots. (My son would like to add that any extra crust is delicious when brushed with melted butter, sprinkled with cinnamon & sugar, and baked!)
To keep the bottom of the crust from puffing too much, line it with a round of parchment paper and cover the parchment with pie weights, pennies, or dried beans.
Partially bake the crust at for 10 minutes. Allow to cool a bit before filling.