In medium bowl, whisk together the first 6 ingredients.
Cut the shortening and butter into smallish pieces (this makes mixing easier.) Using your fingers, pasty blender or two dinner knives, rub or cut the shortening and butter into the dry ingredients until they are the texture of a coarse meal with pea-size pieces.
Gradually stir in the milk with a fork to moisten the dry ingredients. Try not to over work the mixture. If needed add small amount of additional milk to bring it all together.
Form dough into a ball, divide it in half and make into two disks. Wrap individual discs in plastic wrap and refrigerate for at least 2 hours or overnight. Roll out dough on a piece of waxed paper. Carefully flip dough onto pie plate, remove wax paper, tuck dough into place. Patch and smooth any areas that have cracked or broken. Trim as needed. Flute edges. If your fingers are wet this will be easier. Gluten-free pastry dough can be very difficult. If the above is too difficult, or you are in a hurry, just take the dough and press it into place with wet fingers. This can be done either after the dough has chilled or even right after mixing.
For a baked pie shell: Using the tines of a fork, evenly poke holes in the bottom and sides of the crust to prevent it from rising when baked. Bake at 350 degrees until crust is golden brown; approximately 16 to 20 minutes. Check crust during baking to make sure crust is not rising too much. If it is, use a fork to poke additional holes in crust to help release trapped steam.
Makes 2 single 8 or 9 inch crusts.