Dice the cold butter into small cubes or thin slices. Place in the freezer for 5-10 minutes to help keep it cold throughout the duration of mixing the dough.
In a large mixing bowl, whisk together the flour and salt. This ensures the salt is evenly distributed, which helps create a consistent dough.
Add cold butter to the flour mixture and use a pastry blender or two forks, to cut it into the flour. The goal is to create a crumbly texture with some pea-sized pieces of butter still visible. These small butter pockets will melt during baking, creating a flaky crust.
Drizzle in the cold sourdough discard a little at a time, tossing the mixture with a fork or your hands. Continue adding the discard until the dough begins to come together. Grab a handful—if it holds together easily without crumbling, it’s ready. If dry patches remain, add a bit more starter until fully combined.
Using your hands, quickly gather the dough into a dough ball and divide it in half.
Shape each half into a disk and wrap it tightly in a piece of plastic wrap. Chilling the dough for 24 hours to allow for fermentation. If needed right away, chill for at least 30 minutes.
If chilled longer than 30 minutes, let it sit at room temperature for 10–15 minutes before rolling.
Lightly flour your work surface and rolling pin. Roll the dough out to about 1/8-inch thick, turning occasionally to prevent sticking, adding more flour if needed. If cracks form, gently press them back together.
Transfer the rolled-out dough to a pie plate, trim the edges, and fill with your chosen pie filling. Follow your recipe’s instructions for blind baking or baking with filling.