Combine dry ingredients: In a large mixing bowl, whisk together the milled whole wheat flour, salt, and sugar (if using).
Cut in the butter: Grate the unsalted butter or cube the butter and add it to the flour mixture. Using a pastry cutter, fork, or your hands, cut the butter into the flour until the mixture resembles coarse crumbs, with some pea-sized pieces of butter remaining.
Add sourdough starter and 1 tablespoons of ice cold water: Mix in the sourdough discard (or active starter) and 1 tablespoons of water until combined. Use your hands to press the dough together until there are no more bits of flour. If the dough is still dry you can add more water but only 1 tablespoon at a time until you reach the right consistency. The dough should be slightly crumbly but hold together when pressed. It should not be wet.
Chill the dough: Divide the dough into two equal potions. Shape both into a flat discs, wrap them individually in plastic wrap, and refrigerate for at least 2 hours (or overnight for a long fermentation--see tips) to allow the dough to rest and the flavors to develop.
Roll out the dough: After chilling, lightly flour your surface. Roll the pie dough out with a floured rolling pin to about ⅛ inch thick, large enough to fit into a 9-inch pie dish. Use your rolling pin to roll the dough up to easily transfer the dough to the pie dish.
Transfer to pie dish: Carefully transfer the rolled dough to the pie dish. Trim any excess dough around the edges and crimp the edges for a decorative finish. I prefer to use my fingers and thumb to create a beautiful ripple effect, but a fork pressed into the edge looks great too!
Blind bake (if necessary): If your pie recipe requires a blind-baked crust, use a fork to poke holes in the bottom, line the crust with parchment paper, and fill with pie weights or dried beans. This is a must! Otherwise the pie crust will shrink. Bake at 375°F for 15-20 minutes until lightly golden.
Fill and bake: If making a filled pie, add your filling and bake according to the instructions for your pie recipe.