Chill the butter and shortening in the refrigerator for 15 minutes.
Combine the flour and salt in a large bowl and whisk to blend. Scatter the butter and shortening on top. Using a pastry blender, cut the fat into the flour mixture until it becomes small, split pea–size pieces. Sprinkle with half of the water. Using a large fork, mix the dough briskly. Sprinkle with the remaining water and mix until the dough pulls together. See Finishing Steps.
By food processor:
Chill the butter and shortening in the freezer for 15 minutes.
Combine the flour and salt in the processor, cover, and pulse four or five times, to mix. Scatter the chilled butter and shortening on top. Cover and pulse eight to ten times more in 1-second bursts to break the fat into very small pieces. Using the feed tube, add the water in an 8- to 10-second-long stream, while pulsing. Continue to pulse until the dough forms large, clumpy crumbs. See Finishing Steps.
Turn the dough out onto a lightly floured work surface and pack it into a ball. Gently knead once or twice, then flatten into a ½-inch-thick disk. Wrap in plastic and refrigerate for 1 to 2 hours before rolling.