In the bowl of your food processor, add your flour, and salt. Pulse briefly to mix.
Add butter, 1 stick worth at a time. Pulse several times between additions. Pulse a few times until the largest pieces of butter about about pea-sized.
Add ⅓ cup of cold buttermilk and pulse again to mix. Then add additional buttermilk one tablespoon at a time, testing the batter each time. You want to the dough to mold together like a slightly dry playdough. Don't add too much liquid. A coupld of dry spots are okay.
Carefully empty the crumbly dough from the food processor onto a clean, dry surface. Divide the dough into two mounds, approximately 60/40. (70/30 for cast iron)
Gently form the dough into balls. Knead it just enough to that it holds together without falling apart. Do not over knead as it will make a tougher crust. If you see small flecks of butter through your dough that is a good sign of flaky tastiness to come!
Wrap each ball of dough with plastic wrap and refrigerate for one hour (or overnight if you're preparing in advance).
Preheat oven to 350°F
When ready, place the larger dough on a lightly floured surface and roll into a circle until approximately ⅛ of an inch thick.
Carefully place your rolled out crust on a lightly buttered pie tin or pan or skillet. (See notes for skillet instructions). Using a pair of kitchen scissors, trim the dough to apprixmately ½ to ¾ of an inch from the edge of the pie pan.
Add your filling (See notes if you are pre-baking a crust).
Roll out the smaller dough and place on top of the filling. Trim excess dough within ¾" of the rim of the pan. Fold the edge of the rop piece of dough over and under the edge of the bottom piece of dough, pressing together.
Press edges with fingers or with a fork to form edge crust.
Score the top of the pie (if not making a lattice) so that steam can escape.
Optional, brush top of pie with egg wash for a lovely golden brown sheen. (egg wash is 1 egg with 2 Tbsp water)¾
Bake for 45-75 minutes, or until crust is fully baked and browned. (Depends on thickness of crust and fillings)
Allow to cool for at least 1 hour before serving.