Place the flour, cornmeal, salt, and sugar in the bowl of a food processor, and pulse several times to combine. Add the butter, and process, until the mixture resembles coarse meal, about 10 seconds. With the machine 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 out dough onto a clean work surface. Divide in half, and place each half on a piece of plastic wrap. Flatten each to form a disk. Wrap, and refrigerate at least 1 hour or up to 1 day before using.