Process flour, salt and baking powder for 10 seconds to integrate. Add unsalted butter and shortening and five 15-20 short pulses until mixture resembles coarse corn meal. Any balls of butter should be no larger than a pea. Sprinke half the ice water and pulse 5-6 times. Add enough ice water to create a dough that will hold together but not to be sticky. Do not allough dough to form a ball in the mixer.
Turn the dough out into a floured surface and roll into a ball. Flatten dough into a 6" disc and refrigerate for at least one hour before rolling out to 1/8" for use.
Dough will keep 3 days refrigerated or up to a month in the freezer.