In a large bowl, whisk together the flour and salt. With a pastry cutter or your fingers, gradually work the butter into the flour until dime-sized pieces form. In a small bowl, combine the cold water and apple cider vinegar. Add the mixture 1 tablespoon at a time, mixing gently in between each addition. Stir together until the ingredients are incorporated and the mixture holds together when pinched together with your fingers. Turn the mixture out onto a clean countertop and knead 4-5 times until combined. Divide into 2 evenly sized balls and flatten each to a disk shape (with minimal cracks). Wrap with plastic wrap and refrigerate for 2 hours (or up to 2 days). Proceed with your pie recipe's baking instructions from here!