Make the crust: Preheat the oven to 350°F. In a large bowl, whisk together the flours. Add the butter and, using your fingers, rub it into the flour, breaking it down into pea-size pieces so you have what resembles a coarse meal. Dribble 3 tablespoons of the ice water over it and, using your hands, stir to incorporate the liquid so you begin to form a dough. Continue to add more water, 1 tablespoon at a time, just until the dough comes together; it shouldn’t be too crumbly or dry. You may need to add up to 3 tablespoons more, but be careful that the dough doesn’t become too wet or sticky.