Sift together the all-purpose flour, cake flour, and salt into a large mixing bowl. Dice 6 tablespoons of the chilled butter, returning the remaining butter to the refrigerator to keep cold. Place the diced butter into the mixing bowl and using your fingers or a pastry blender, blend until the mixture forms a coarse meal, similar to a piecrust. Make a well in the center of the mixture and add the water. Use a rubber spatula to gradually blend the water with the flour mixture, mixing just until a rough, sticky dough is formed. Wrap dough in plastic wrap and refrigerate for 1 hour.
Place the remaining butter on a work surface, (a marble surface is ideal). Using a rolling pin or the heal of your hand, smash the butter into the surface until pliable, taking care not to over work the butter as it should stay chilled. Work butter into a 5-inch square.
Remove the rested dough from the refrigerator and place on a lightly floured work surface. Roll out dough into a 12-inch circle, being careful not to pull or tear the dough. (The dough mixture may still be very rough and tacky.) Place the butter square into the center of the circle and fold the edges of the dough over the butter, pressing to seal the edges. You should now have a square of butter wrapped in dough.
Using a rolling pin, roll the square into a 16 by 8-inch rectangle. (The dough may need to be pounded with the rolling pin several times to allow the butter to become more pliable.) Be careful not to tear the dough. Fold the rectangle 3 times as you would fold a business letter. Place the rectangle in front of you lengthwise and roll into another 16 by 8-inch rectangle. Fold again 3 times as you would a business letter and make 2 small indentations into the dough to remind yourself that it has been rolled twice. Wrap the dough in plastic wrap and refrigerate for 1 hour.
Return the rested dough to a lightly floured surface and repeat the process of rolling the dough into a rectangle, making 3 business-letter folds, 2 times. Make 4 small indentations into the dough to remind yourself that it has been rolled a total of 4 times. Wrap the dough in plastic wrap and refrigerate for at least 1 hour. If desired, dough can rest refrigerated for up to 2 days at this point.
Remove the dough from the refrigerator and place on a lightly floured work surface. Roll into a 16 by 8-inch rectangle and fold 3 times, similar to a business letter. Repeat process and make 6 small indentations into the dough. Wrap and refrigerate for 2 hours. Now the pastry is ready to be rolled and used in the desired puff pastry recipe.
Yield: about 2 1/2 pounds