In a large bowl, combine flour with salt and sugar.
Work in the butter, being careful to not over mix.
Add in the starter and stir until combined.
Divide the dough in two and shape each half into a disk and wrap in plastic wrap. Chill in the fridge for at least 2 hours or up to 3 days.
Sprinkle a clean countertop with flour and roll out the dough until it is approximately 12″.
Drape it over a 9″ pie plate.
Add pie filling.
Roll out the other half and drape it over the filling
Trim the excess.
Optional: Crimp the edges and add design to the middle for steam release.
Notes
You can use active sourdough starter or discard.
You can cover with towel and allow to sit at room temperature to ferment for at least 8 hours or overnight, then refrigerate or freeze for a few hours before rolling out and baking. But I recommemnd just fermenting in the fridge for a few days to give a flakier crust.