Cold unsalted butter, cut into quarter-inch pieces
Cold vegetable shortening, cut into quarter-inch pieces
Using an electric mixer: Combine flour, sugar and salt in a large bowl. Add the butter, tossing it with the flour. With the mixer on low speed, blend the butter into the flour until you have what looks like coarse, damp meal, with both large and small clumps. Add the shortening and repeat. Turning the mixer on and off, add half of the water, mixing slowly until the dough starts to form large clumps
By hand: Combine the flour, sugar and salt in a large bowl. Toss well, by hand, to mix. Scatter the butter over the dry ingredients and toss to mix. Using a pastry blender, 2 knives, or your fingertips, cut or rub the butter into the flour until it is broken into pieces the size of small peas. Add the shortening and continue to cut until all of the fat is cut into small pieces. Sprinkle half of the water over the mixture. Toss well with a fork to dampen the mixture. Add the remaining water, 1 and a half to 2 tablespoons at a time, and continue to toss and mix, pulling the mixture up from the bottom of the bowl on the upstroke and gently pressing down on the downstroke. Dough made by hand often needs a bit more water. If necessary, add water 1 or 2 teaspoons at a time untili the pastry can be packed.
Take the pastry and, using your hands, pack it into a ball as you would pack a snowball. Knead the ball once or twice, then flatten the ball into 3/4-inch-thick disks on a floured work surface. Wrap the disk in plastic and refrigerate for at least an hour or overnight before rolling.