In a food processor, place flour, cornmeal, salt & sugar; pulse several times to combine. Add butter; process until mixture resembles coarse meal, about 10 seconds. While machine is running, pour the ice water through the feed tube in a slow, steady stream, until the dough just holds together (do not process for more than 30 seconds). Turn the dough out on work surface. Place dough on plastic wrap. Flatten to form disk; wrap & refrigerate at least 1 hour.