Use a cheese grater to grate the cold butter into a large mixing bowl. Add the flour, salt and sugar and use a fork to toss the ingredients together, making sure the butter is coated and separated. Use a bench scraper or a pastry cutter to cut the butter into the flour mixture, until it forms large crumbles.
Add the sourdough discard and vinegar to the bowl and then use a fork to incorporate them into the mixture. Switch to your hands and press the dough together until there are no dry bits left in the bowl. (If the dough is too dry, add a teaspoon of ice water.)
Form the dough into a disk shape and wrap in plastic wrap. Use a rolling pin to flatten the disk. (This will help smooth the edges.) Chill for at least 2 hours or up to 4 days.
Proceed with your pie recipe directions.
The dough can be stored wrapped in plastic wrap for up to 4 days in the fridge or up to 3 months in the freezer.