In a medium bowl, whisk together the flour, sugar, and salt. Add the cold cubes of butter and use a pastry cutter to work the butter until it is the size of peas. Add the buttermilk and stir to combine using a wooden spoon. Once a shaggy dough starts to form, dump the dough on to a lightly floured surface and knead into a flat disc. Cover with plastic wrap and refrigerate for an hour.

Preheat the oven to 350 degrees F.

Add the sugar and the grated apple to a large mixing bowl. Mix together using your fingers until the sugar is clumpy and fragrant. Add the flour, salt, nutmeg, and cinnamon. Whisk to combine.

Whisk together the buttermilk and the eggs in a small mixing bowl. Whisk in the cider and vanilla extract. Add the wet ingredients to the dry and whisk to combine.

Remove the crust from the refrigerator and remove the plastic wrap. Roll out on a lightly floured surface until the dough is about a 10 inch circle. Trim the edges to make it more of a perfect circle. Butter a 9 inch pie dish, place the dough inside the dish, press into the bottom and then crimp the edges between two of your fingers. Pour the filling into the crust and then bake for 55-60 minutes until no longer jiggly in the center.

Let the pie cool completely before serving. I find it best if chilled in the refrigerator overnight before serving.