Chill the dough and let it rest before rolling into a crust. The fat is most important. It tenderizes the dough by coating the starch granules, keeping gluten from developing, while larger pieces separate layers of dough to provide flakiness. Unsalted butter is my favorite for flavor but makes a less-flaky crust. Lard produces the flakiest crust with good flavor but is high in saturated fat.
Vegetable shortening performs like lard with less saturated fat.
The best for flavor and flakiness without the saturated fat is to blend unsalted butter and vegetable shortening. Apples can be refrigerated for a week or two or stored in a cool, dry, well-ventilated place for longer periods. When the dough just starts to hold together, turn it onto a piece of parchment paper or plastic wrap, then press into two rounds about 6 inches in diameter. Wrap well and refrigerate about 20 minutes before continuing. Roll out the dough on a cool, floured surface.