Mix the dry ingredients: In a large mixing bowl, whisk together all-purpose flour, salt, and sugar.
Cut in the butter into chunks: Add the cold butter chunks to the bowl. Use a pastry cutter, pastry blender, or even a food processor to work it into the dry ingredients until the butter pieces are about the size of peas.
Add the starter: Stir in your active sourdough starter or sourdough discard into he flour/butter mixture. Use a wooden spoon to combine.
Add ice water: Drizzle in ice water until the pastry dough just comes together. Avoid over mixing. The key to a tender pie crust is minimal handling.
Chill the dough: Create a ball with the dough. Cut the dough in half, and make two discs. Wrap them in a piece of plastic wrap. Chill at least 1 hour for a single crust pie, or overnight for a flakier crust and more sourdough flavor and fermentation.
Roll the dough: On a lightly floured surface, use a floured rolling pin to roll the dough into a circle large enough for your pie plate. Transfer to the pie dish, trim excess dough, and crimp edges.
Blind baking (if needed): For blind bake crusts (like in pumpkin pie or custard pie recipes), line the bottom crust with parchment paper and fill with pie weights or dry beans. Bake until lightly golden brown.
Fill and bake: Add your pie filling for double-crust pie or single-crust pies, cover with top crust if using, brush with egg wash, and bake until golden brown.