Add the salt and butter to the flour. Rub them together, then add the milk, and, if necessary, a little water, making a stiff dough. Place the dough on a firm table or block, and beat it with a mallet or rolling-pin for fully half an hour, or until it becomes brittle. Spread it half an inch thick; cut it into small circles, and prick each one with a fork. Bake them in a hot oven about twenty minutes.