Combine dry ingredients. In a large bowl add the flour, sugar, and salt. Stir to combine.
Add butter. Add in the grated unsalted butter. Using a pastry cutter or a fork, cut the butter into the flour mixture until it resembles crumbs. You can also use a food processor for this step.
Add sourdough discard. Add the cold sourdough discard into the flour mixture. Using a spatula, pastry cutter, or fork incorporate it into the flour mixture. Using a spatula is the easiest way to incorporate the discard into the flour mixture.
Shape and chill. Form the dough into a round disc or rectangle. Wrap the pie crust in plastic wrap and allow it to rest in the fridge for 2-12 hours. Overnight is best but it can be stored for up to 3 days.
Preheat oven. Preheat the oven to 375 degrees F.
Roll out. Remove the dough from the fridge and divide it evenly in two. Roll one part out into an 11-inch round or large rectangle. Fold and pinch the edges, then place it in a 9-inch pie pan. *This recipe makes 2 crusts, so you can use the other half to top your pie with a lattice top, fully covered, or make another single-crust pie.*
Bake. Bake the single pie crust at 375 degrees F for 20 minutes for a baked pie shell. If this is a filled pie it can bake up to 65 minutes depending on the filling.