1. Preheat oven to 400 degrees. Prick bottom of pie shell all over with a fork. Line with foil; fill with dried beans or pie weights. Bake until edges are lightly browned, about 25 minutes. Remove the foil and weights, and bake until crust is lightly browned, about 10 minutes more. Let cool completely on a wire rack.

2. Reduce oven heat to 350 degrees. In a medium bowl, whisk together buttermilk, butter, egg yolks, and vanilla. In a large bowl, combine sugar, flour, and salt. Whisk into dry ingredients. Pass through a fine sieve into a clean bowl. Whisk in lemon zest.

3. Pour mixture into pie shell; bake until center is just set, about 1 hour and 10 minutes. Let cool, and then refrigerate at least 4 hours. Serve cold with berry sauce.