Measure the flour by scooping a dry-measure cup into the container and sweeping off the excess with a knife. Place 3½ cups of the flour in a mixing bowl. Refrigerate the remaining ½ cup of flour.
Dissolve the salt in 1 cup of the ice water, and then gradually stir the ice water into the flour. When all the flour is moistened and is just beginning to hang together in a ragged dough, stop adding water. Turn the dough out onto your work surface and gather it into a ball. The dough may be crumbly; it will certainly look awful; this is as it should be. Wrap the dough in plastic or a bag, and refrigerate for 1 hour or longer.
Remove the dough from the refrigerator, lightly flour your work surface, and roll out the dough very evenly into a square about 12 × 12 inches.
Remove the butter from the refrigerator and unwrap it. Beat it with a rolling pin a few times to soften it. Sprinkle it with the chilled ½ cup flour. Mash and knead the butter further, using the rolling pin and the heel of your hand, until it is smooth and creamy and all the flour is incorporated. This should not go on so long that the butter begins to melt. (To keep your hands from becoming too warm, you can dip them in cold water for about 1 minute, then dry them, before kneading in the flour. Your goal is to get the butter and the dough as close to the same texture as possible. Form the butter into a rectangle.
Fold the square of dough in half. Center the rectangle of butter on the folded dough and fold the long sides of the dough over it, enclosing it completely. Pinch to seal. Gather the dough around the ends and pinch to seal. Sprinkle it very lightly with flour and turn it over, seam side down. Roll it out gently into a rectangle and fold it one third of the way over itself. Fold the other end over this, as if folding a letter.
Rotate the dough 90 degrees and roll it out again into a rectangle 20 × 24 inches. Again fold one end one third of the way in, and then fold the other end over that. You now have the “letter” of dough again. Gently press the ends of 2 fingers into the dough; you have made 2 of the 6 turns, and this will mark it so you don’t forget. Rewrap and refrigerate it for at least 1 hour.
Remove the dough from the refrigerator once more and unwrap it. If it is very cold, let it stand for 10 minutes or so before rolling, otherwise the hardened butter may tear its way out of the package. Lightly flour the work surface and again roll out the dough into a rectangle 20 × 24 inches. Form the “letter,” roll out again, and again fold it in thirds. Mark the dough with 4 depressions; you have completed 4 of the 6 turns. Rewrap and refrigerate the dough for at least 1 hour.
Repeat step 7. The dough has now been turned 6 times and is ready to be shaped and baked. It can also be rewrapped and refrigerated for a few days or frozen for up to several weeks at this point.