In a food processor, pulse together flour, salt, and sugar to combine. Add butter, and process until mixture resembles coarse meal, about 10 seconds. With machine running, add 1/2 cup ice water in a slow, steady stream through the feed tube, just until dough holds together. Test dough by pinching a small amount; if it is still crumbly, add up to 1/4 cup more ice water, a little at a time. Do not process more than 30 seconds.
Turn out dough onto a clean work surface, and divide into 3 equal pieces. Place each piece on plastic wrap, and flatten into a disk; wrap tightly. Refrigerate at least 1 hour before using.