In a large mixing bowl, combine your flour, starch, xanthan gum, and salt. Mix well to combine.
Now add your shortening and work to bring together with a pastry cutter or a food processor. Mix until crumbs form and it looks like sand.
Now add the apple cider vinegar and the water. I can't give an exact amount as it depends on what flour blend you use and how humid it is when you are making this mix. You want your dough to come together and be tacky, but not sticky. If it is too dry, add more water. If it is too wet, add more flour, a spoonful at a time.
If you are rolling this dough, roll between two sheets of parchment paper. Chill after rolling. Let dough warm for 5 minutes on the counter after chilling but before trying to shape dough.
If you are pressing into a pie pan, no resting is required.
To make it dairy free: Use an equal amount of plant-based butter of choice or vegetable shortening or lard. To make it sweeter: Add up to 3 tablespoons of white sugar. To make it savory: Add dried or fresh herbs of your choice. I love thyme and rosemary for holiday baking! LivingBeyondAllergies.com