Classic Gluten Free Apple Pie

Double Pie Crust 3 cups (420 g) all purpose gluten free flour (I highly recommend Cup4Cup, my Better Than Cup4Cup blend, or my Mock Cup4Cup), plus more for sprinkling

xanthan gum (omit if your blend  already contains it)

baking powder

kosher salt

unsalted butter, roughly chopped and chilled

to 1 cup cold water, iced (ice cubes do not count in volume measurement)

Pie Filling 3 pounds medium-size Granny Smith apples, peeled, cored and sliced about 1/4-inch thick

granulated sugar

kosher salt

(9 g) tapioca starch

ground cinnamon

For Finishing Egg wash (1 egg + 1 tablespoon cold water, beaten) (optional)

Large paper grocery shopping bag, plus a stapler