Put flour and salt in bowl of machine. Cut butter and margarine into flour. Process a few seconds until mixture resembles coarse meal.
Drop by drop add the water, processing very briefly. The whole process would take 20 to 30 seconds.
Wrap and chill the pastry for at least 1 hour.
Preheat oven to 425 F. 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 the rolling pin. Roll pastry in one direction only, turning pastry continually to prevent it from sticking to the surface.
If you are doing a deep dish pie plate, you could use both pieces of dough (that’s what I did). If not, store second portion of dough wrapped in plastic for another pie.
Using pie plate as a guide, measure rolled-out pastry -- it should be slightly larger than the pie plate and ⅛-inch 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 edge. Fold edges over and flute. Line the dough with foil paper and fill the dough with dried beans or pie weights. Bake at 425 for 10 minutes.
Remove the weights and the foil paper and bake another 10 minutes (or until golden). Cool completely on a wire rack.