Combine the first 2 ingredients in a small bowl to make the seasoning mix.
Combine the all-purpose flour, corn flour, sugar, salt, and seasoning mix in an electric mixer equipped with a dough hook and process until well blended. Add the cold shortening and blend at low speed, scraping the sides and bottom of the bowl, until the ingredients just come together and resemble very coarse meal or dried split peas. Gradually add the very cold water and continue to process at low speed just until the water is absorbed, being careful not to overmix. As soon as the liquid is absorbed, gather the dough into a ball, and refrigerate until cold, at least 4 hours, preferably overnight.
When you're ready to form the crusts, divide the dough in half and form each half into a ball. Liberally flour your hands, the working surface and the rolling pin. Place one of the dough balls on the floured surface and roll it out, keeping it as even and round as possible. Turn the dough as you roll, and dust with flour as necessary, until the circle is about 11 inches in diameter. Carefully fit the circle into a 9-inch pie tin and crimp the edges with your hands or with the tines of a fork. Repeat with the remaining ball of dough. If the shells are to be filled before baking, they are now ready for use.
If the shells are to be baked before filling, preheat the oven to 300o. Use the tines of a fork to make a series of little air holes in the shells (so they will not bubble while baking), and bake them until lightly browned, about 20 minutes.