Measure out the flour, cornstarch, sugar, and salt and place in the freezer to cool for ten minutes.
Cut the butter into half-inch cubes and place in the freezer to cool.
Combine the milk and vinegar in a liquid measuring cup and stir to combine. Place in the fridge until ready to use
Place the chilled dry ingredients in the bowl of your food processor fitted with a metal blade and pulse once to combine.
Add the butter to the food processor.
Have the milk mixture ready and turn the food processor on. After a few seconds, slowly pour the milk mixture down the feed tube of the food processor. Once all of the milk has been added, turn off the food processor.
Turn the dough out onto a piece of cling film and shape into a flat disc. Wrap the dough tightly and place in the fridge to cool for at least one hour.
Take half of the dough and turn out onto a floured work surface. Using a rolling pin, roll out to a thickness of roughly 1/4" and a diameter of 13." Lay into a 9" pie tin and place in the fridge to chill for another 2 hours.
Trim the excess dough off with a paring knife and press down the edges with the tines of a fork. Prick the dough all over with the tines of a fork
Place a sheet of parchment paper on the dough and then fill with pie weights or uncooked beans over the top. Bake for ten minutes and then remove the pie weights. Bake for another 12 minutes or until edges are golden brown and center is a light golden color. Let the pie crust cool to room temperature