Preheat oven to 450 degrees. Prepare pastry and line 9-inch pie plate. Place a piece of double thickness foil lightly over the pastry to prevent over-browning. Bake 8 minutes. Remove foil. Bake 4 to 6 minutes more or until crust is lightly browned; cool. Reduce oven temperature to 350 degrees.
In saucepan, melt butter over medium-low heat. Stir in sugar and flour. Remove from heat; set aside.
In mixing bowl, beat eggs until fluffy (about 1 minute). Stir in buttermilk and vanilla.
Gradually whisk buttermilk mixture into butter mixture until smooth. Pour into prebaked crust.
Place pie on oven rack; carefully tent whole pie with foil. Bake 50 to 55 minutes or until center is set when gently shaken. Cool on wire rack for 1 hour. Cover; refrigerate at least 4 hours before serving.