1. Make the dough package: Whisk together flours and salt in a large bowl. Using your fingers, incorporate butter until mixture resembles coarse meal.

2. Form a well in center; pour in cold water. Using your hands, gradually draw flour mixture over water, covering and gathering until mixture begins to come together. In bowl, knead until dough just comes together, about 15 seconds. Pat into a rough ball; turn out onto plastic wrap. Wrap tightly; refrigerate 1 hour.

3. Make the butter package: Sprinkle 1 1/2 teaspoons flour on a piece of parchment paper. Place sticks of butter on top; sprinkle with remaining 1 1/2 teaspoons flour. Top with parchment. Using a rolling pin, pound butter to soften and flatten to about 1/2 inch thick. Remove top parchment; fold butter package in half onto itself. Replace top parchment; pound until butter is 1/2 inch thick. Repeat 2 or 3 times, or until butter becomes quite pliable. Using your hands, shape into a 6-inch square. Wrap well in plastic; refrigerate until cold, up to 10 minutes.

4. Roll dough: Place dough package on a lightly floured work surface. Gently roll dough into a 9-inch round. Place butter package in center of dough round. Using a paring knife or bench scraper, lightly score dough to outline the butter square; remove butter, and set aside. Starting from each side of the center square, gently roll out dough with the rolling pin, forming four flaps, each 4 to 5 inches long; do not touch the raised square in center of dough. Place butter package on center square. Fold flaps of dough over butter to enclose. Press to seal.

5. Using the rolling pin, press down on dough at regular intervals over entire surface until it is about 1 inch thick. Gently roll out into a rectangle, about 9 by 20 inches, with one of the short sides closest to you. Keep corners even by squaring them with the side of the rolling pin or your hands. Brush off any excess flour. Starting at the near end, fold the rectangle in thirds as you would a business letter; this completes the first single turn. Wrap in plastic; refrigerate 1 hour.

6. Repeat step 5, giving it 5 more single turns. (Always start with the flap opening on the right.) Refrigerate 1 hour between each turn. After the sixth and final turn, wrap in plastic; refrigerate at least 4 hours or overnight before using.