In a double boiler, melt the chocolate chips over a low heat, stir constantly until smooth.
In a mixing bowl, whisk sugar, flour and salt to combine.
In another mixing bowl, combine eggs, buttermilk and vanilla; add sugar mixture and beat with a mixer until well combined.
Pour the batter into the pie crust (you may have leftover batter).
Bake, on the middle oven rack, for 1 hour 15 minutes to 1 hour 25 minutes or until the pie is crisp on the top and/or inserted knife into center of pie comes out with just a little bit of moist chocolate.
Cool; refrigerate immediately if not eating pie until later or let pie stand at room temperature for 1 hour, prior to eating.