Make your homemade pie crust and place in a 9 inch pie plate. If using premade frozen, unthaw. Preheat your oven to 375 degrees.
In the bowl of an electric stand mixer beat eggs and sugar until light yellow in color, the mixture will be slightly thick. Beat the flour in first, then the buttermilk, melted butter, lemon zest, lemon juice, and vanilla.
Pour the mixture into you unbaked pie crust. Bake at 375° for 20 minutes. Reduce the oven temperature to 325° and continue baking until the center is set and barely jiggles, about 20 to 25 minutes longer. Cool on rack.