Preheat oven to 325°. Position a rack in the center of the oven.

Melt chocolate chips in a saucepan/double boiler and melt over low heat, stirring constantly. (I actually melt them in the microwave: 30 to 40 seconds, stir and go again for 30 to 40 seconds until melted.)

In a medium bowl, whisk together the sugar, flour, and salt until well combined. In a large mixing bowl, combine the eggs, buttermilk, and vanilla. Add the sugar mixture and mix with an electric hand mixer or whisk vigorously. With a rubber spatula, stir the melted chocolate into the batter.

Pour batter into the pie crust. Place pie in the oven on the middle rack. Bake for 1 hour and 15 minutes to 1 hour and 25 minutes, or until the pie is crisp on top and a knife inserted in the center comes out with just a bit of moist chocolate on it.

Remove from the oven and cool completely. Let stand at least 1 hour before serving.