Preheat oven to 350°F. Set the pie shell on a baking sheet.
In a mixing bowl, cream together the sugar, butter, and vanilla. Mix in the flour. Pour the buttermilk and eggs, and whisk or beat until everything's blended together.
Pour the filling into the pie shell. Bake the pie (on the baking sheet) for 40 to 45 minutes, until the top puffs slightly and turns golden brown. (If the crust browns too quickly, shield it with a ring of foil for the last 10 minutes of cooking.) Cool for 30 to 60 minutes before serving warm, or store the cooled pie in the refrigerator until ready to serve.