Add flour, sugar, xanthan gum and salt to a food processor and pulse to combine. Add cold diced butter and pulse until mixture resembles coarse crumbs.

Add egg, cold water and apple cider vinegar to a small bowl and use a fork to beat together the egg and mix. Pour egg mixture into food processor and pulse a few more times until dough is just moistened.

Transfer the pie dough to a glass bowl and use clean hands to shape it into a ball, slightly flattened. Cover the bowl with plastic wrap and place in the fridge to chill for at least 1 hour.

Remove chilled pie dough from refrigerator and place on counter for about 15 minutes.

Transfer pie dough to a lightly floured piece of parchment paper. Sprinkle a little flour on top of the dough and add an additional piece of parchment paper on top. Roll out the dough with a rolling pin into a 12 inch circle.

Transfer the dough to an ungreased pie pan and press into place - flattening the crust against bottom and sides as well as touching up any cracks. Trim off any excess crust and crimp or flute the edges.

Fill and bake as directed per your pie recipe.