Prepare the crust: Combine flour and salt. Cut in shortening until mixture resembles coarse crumbs. Gradually add ice water, mixing until dough forms. Chill for at least 30 minutes.
Roll out the dough and place in a 9-inch pie plate.
Prepare the filling: Whisk together sugar, cornstarch, and salt. In a separate bowl, whisk together buttermilk, eggs, melted butter, and vanilla extract. Gradually add the wet ingredients to the dry ingredients, whisking until smooth.
Pour the filling into the pie crust.
Bake at 350°F (175°C) for 45 minutes, or until the filling is set and the crust is golden brown.
Let cool completely before serving.
Notes
For a richer flavor, use whole milk instead of buttermilk. You can also add a sprinkle of nutmeg or cinnamon to the filling.