Make the pastry: in a bowl, whisk together the flour, sugar, and salt.
Cut in the shortening with a pastry blender until the shortening resembles small peas.
Add the milk and vinegar and stir with a fork just until the dough begins to come together when a small bit is pressed between your fingers; do not overwork the dough.
Press the dough together to form a ball and knead lightly; shape into a disk and refrigerate, wrapped in wax paper, for at least 30 minutes or up to 2 days.
At least 25 minutes before baking, position oven rack in the middle of oven; preheat to 400°; have ready a 9-inch glass pie plate.
Roll out the dough on a lightly floured surface to an 11-inch circle; transfer dough to the pie plate nad gently press the pastry against the side and bottom of the plate.
Turn the edge under and crimp as desired; prick all over the bottom and side with a fork.
Press a piece of heavy-duty foil snugly into the bottom and against the side of the pastry shell and fill with uncooked beans or rice; bake for 15 minutes, remove the beans and cool the shell on a wire rack.
Decrease oven temperature to 350°.
Make the filling: process the sugar and the zest in a food processor until the zest is finely ground.
Beat the eggs, sugar mixture, and cornmeal with an electric mixer on medium speed in a bowl, just until blended.
Add the lemon juice; beat again until blended.
Pour in the melted butter in a fine stream while the beaters are running and beat just until blended.
Pour the mixture into the pie shell and bake for 40-45 minutes, until just set in the center.
Turn off the oven, open the oven door, and let the pie sit in the oven for 30 minutes.
Serve warm, or refrigerate and serve cold, with the Lemon Whipped Cream.