Line the pie pan with the pie crust. Cut a circle of parchment paper big enough to fit the pan and place on top of the pie crust. Fill the tin with dry beans or pie weights and bake for 8 minutes. Remove the pie weights and paper and bake for another 5 minutes. Remove the pie crust and lower the oven to 350 degrees.
In a saucepan, melt the butter over medium-low heat. Whisk in the sugar and flour until smooth and set aside.
In a large bowl, beat the eggs until they are light and fluffy, then whisk in the buttermilk and vanilla. Temper the egg mixture by gradually adding and whisking it in to the butter mixture. Stir until everything is nice and smooth. Pour the mixture into the pie crust and bake for 50 -55 minutes or until the center is just set but still a little jiggly. Cool on a rack for an hour and then refrigerate for 4 hours or overnight before serving.