Remove the ice water mixture from the refrigerator. With machine running, add 1/4 cup of the ice water in a slow, steady stream through feed tube. Pulse until dough holds together without being wet or sticky; be careful not to process more than 30 seconds. To test, squeeze a small amount together: if it is crumbly, add more ice water, 1 tablespoon at a time, but don't add too much that you end up with a sticky dough.