Cut the butter into ½” cubes and refrigerate. In a large bowl, whisk together the all-purpose flour, whole wheat flour, salt and sugar. Sprinkle butter cubes over the flour mixture and lightly toss to combine. Using a fork or a pastry cutter, work the butter into the flour mixture. Working quickly, use your hands to roughly rub mixture together until butter pieces are about the size of peas.
Make a small well in the middle of the flour & butter mixture. Add 12 tablespoons ice water and, using your hands, gently combine the water into the flour mixture. As the flour begins to hydrate, switch to a gentle kneading motion to continue to combine the flour mixture with the water. The goal is to be able to pick up and squeeze the dough into a ball with your hands, so if the mixture is still too dry, add another 2 tablespoons of water and continue to mix. There’s a lot of dough here, so this step may take some time. Don’t be discouraged, just keep mixing with your hands and adding ice water as necessary until a dough ball forms. Lift dough ball out of the bowl, leaving any dry bits behind. Place on a sheet of plastic wrap.
Add a tablespoon of ice water to any dry bits in the bowl and stir with your hands until a mini dough ball comes together. Combine mini dough ball with the larger ball on the plastic wrap and bring the plastic wrap around the dough tightly. Press down on wrapped dough so that it is in a flat rectangular shape. Refrigerate for at least 8 hours, preferably overnight.