In a medium bowl whisk together the flours, xanthan gum, baking powder, salt and sugar. Cut in the margarine and Crisco with a pastry cutter or two knives in small pieces until you have shortening the size of lima beans (not cornmeal).
In a separate bowl, beat together the egg, vinegar and 3 tablespoons of the ice water with a fork. Pour egg mixture into the dry ingredients and stir with your fork (about 20-30 seconds). Add 3 more tablespoons of ice water and stir for another 20-30 seconds. Continue to add water, 1 tbsp at a time, and stir until there are no crumbs left at the bottom of the bowl (I usually add 2 more tablespoons of the ice water).
Generously sprinkle your pastry cloth with sweet rice flour and rub around so it coats the area you will be working on. Roll your rolling pin through the flour on the cloth so it is fully coated as well.
Divide dough into two halves and roll the first half out so it is about ¼ of an inch thick. Put the pin at one edge of the dough, lift up your pastry cloth and roll it over the rolling pin so the dough rolls up on top of the rolling pin. Lay the pastry cloth back on the counter and continue to roll the rolling pin so the dough is wrapped around it partially (enough so that when you let go, the dough stays on top of the pin). Move your pie plate next to the rolling pin. Lift up the rolling pin, gently holding the dough on top so it does not slide off, and drag the dangling edge so that it is laying about an inch over the edge of the pie plate. Carefully unroll the crust the rest of the way into the pan.
Trim the edges of your crust so it hangs 1 inch over the edge of the pie plate. Lift the over hanging crust and fold under about 1 1/2 inch of the crust so you can see the rim of your pie plate all the way around.
Add the pie filling and roll out the second half of the dough. Either place the second crust over the filling or into another pie plate. Pinch the edges using your thumb and pointer finger on both hands to make a decorative sealed edging.
Bake as directed for the filling used. Put strips of tin foil over the edges of the crust until the last 15 minutes of baking to prevent the crust from browning too much.
For a baked pie shell, prick the pastry with a fork on the sides and bottom. Bake in a preheated 425 degree oven for about 12-14 minutes. Cool before filling. Makes one 2-crust pie or 2 pie shells.