In a food processor or by hand, mix butter and flour until butter is fully incorporated.
Add sourdough starter, cold water, and salt. Pulse or mix until dough forms a uniform ball, adding just enough water to avoid density.
Divide dough into two portions: about 250g for bottom crust and 200g for top crust.
Flatten each dough ball into a round disk and wrap tightly with plastic wrap or bees wrap.
Ferment either on the counter for 8-12 hours then refrigerate, or cold ferment in the fridge for 4 hours to one week.
Remove from fridge and let rest 10 minutes before rolling out.
Bake crust according to your pie recipe's directions.
