Mix dry ingredients.
In a large mixing bowl, whisk together flour and salt.
Cut in butter.
Add cold, cubed butter. Use a pastry cutter or fingertips to work it into pea-sized pieces. A few larger chunks help create flaky layers.
Add sourdough starter.
Stir in starter with a fork. Sprinkle in cold water 1 Tbsp at a time, mixing just until the dough clumps together. It should be shaggy, not sticky.
Shape and chill.
Turn dough onto a lightly floured surface. Divide in two, shape into discs, and wrap tightly in beeswax wrap or plastic. Refrigerate at least 2 hours (up to 4 days). The flavor deepens the longer it rests.
Roll and use.
Let dough sit at room temp 10–15 minutes before rolling. Roll to fit a 9-inch pie plate.
