Cut 8 ounces (2 sticks) butter into 1/2 to 1/4-inch dice, place on a plate and refrigerate while preparing remaining ingredients.Measure water and add salt; stir to dissolve and set aside.
Coarsely dice remaining 4 tablespoons (1/2 stick) butter. Place flour in work bowl of food processor fitted with metal blade; add 4 tablespoons butter and pulse until butter is absorbed -- about ten to twelve 1-second pulses.
Add remaining butter and pulse once or twice to distribute. Add water and pulse 3 or 4 times, just until dough forms a rough ball. Do not over-process.
Flour work surface and scrape dough from work bowl. Shape dough into a rough rectangle and place between 2 pieces of plastic wrap. Press dough with rolling pin to flatten, then roll back and forth several times with rolling pin to make a 12 by 18 inch rectangle of dough.
Peel away plastic wrap and invert dough to floured work surface. Peel away second piece of wrap. Fold dough in thirds in the width, folding the top third down and the bottom third up, to make a 6 by 18-inch rectangle, then roll up the dough from one of the 6-inch ends, making sure to roll end under dough. Press the dough into a square, wrap in plastic and refrigerate 1 hour, or until firm.