Combine flour, sugar, and salt in a medium bowl. Add cubed cold butter to the dry mix and coat the butter cubes with flour. Then use a pastry cutter, fork, or your fingers to work the butter into the flour mixture until it’s in pea-sized pieces.
Combine water, apple cider vinegar, and ice in a separate bowl. Add the liquid to the dry stuff a tablespoon at a time until the dough just comes together with some crumbs on the edges. You should need 4-6 tablespoons of the liquid.
Shape the dough into a round disc, adding more liquid in small drops if needed to get the dough to stick. Once the dough is in a solid disc, wrap it in plastic wrap and store it in the fridge for at least an hour, but overnight is best.
When ready to make pie, Preheat oven to 425 degrees F.
Roll pie crust out on a lightly floured surface until it’s roughly 10 inches in diameter. Transfer to your pie pan and trim edges to your liking. Poke some holes in the crust with a fork and line the pie with parchment paper or foil. Then add pie weights or dry beans to the crust.
Bake the crust for 15 minutes at 425 degrees F.
For filling:
Whisk together sugar and flour in a medium bowl. In a separate bowl, whisk together buttermilk, eggs, melted butter, lemon juice, lemon zest, and vanilla. Whisk wet ingredients into dry ingredients until mixture is smooth.
Pour filling into cooled pre-baked pie crust. Adjust oven to 350 degrees F.
Bake pie at 350 degrees for 40-45 minutes until center is set.
Let pie cool for 45-60 minutes before slicing and serving. Store leftover pie in the fridge for up to five days.