In the work bowl of a food processor, place flour, sugar, and salt; pulse until combined. Add cold butter, and pulse until mixture is crumbly.

In a small bowl, whisk together cold sour cream and 4 tablespoons (60 grams) ice water. With processor running, add sour cream mixture in a slow, steady stream just until dough comes together; add up to remaining 1 tablespoon (15 grams) ice water if mixture is too dry. (Mixture may appear crumbly. It should be moist and hold together when pinched.) Turn out dough, and shape into a disk. Wrap tightly in plastic wrap, and refrigerate for at least 30 minutes.