In a large bowl, sift the flour and salt. Cut the chilled butter and margarine into 1 tablespoon bits and add to the flour. With a pastry cutter, work flour and shortening together until mixture resembles coarse meal. Add the ice water little by little, pressing the pastry together into a ball. Wrap and chill for at least 1 hour.

(It is important to work the pastry as little as possible. Don't overhandle. A secret to light, flaky pastry is to keep the mixture cool, add as little water as possible, and mix only as much as necessary.)

If pastry has been chilled for a long time, let it sit at room temperature for at least 15 minutes before rolling.

Lightly flour a pastry board, marble counter, or kitchen counter. Divide the pastry in half. Pat each piece of pastry into a flat round. Lightly flour rolling pin. Roll pastry in one direction only, turning pastry continually to prevent it from sticking to the surface.

Using pie plate as a guide, measure rolled-out pastry ~ it should be slightly larger than the pie plate and 1/8-inch (2 mm) thick. Fold rolled pastry circle in half so you can lift it more easily. Unfold, gently fitting the pastry into the pie plate, allowing pastry to hang evenly over the edges. Do not trim the pastry yet.

Fill the pie with filling. The roll out the second crust in the same manner as for bottom. Fold circle in half and with a sharp, pointed knife cut little vents in a decorative pattern. Place folded pastry on one half the pie. Unfold, pressing top and bottom pastry together. Trim edges with scissors, leaving a 1/2-inch (1 cm) overhang. Fold bottom pastry overhang over top and press firmly to seal. Crimp rim, using fingers or the tines of a fork.