Pie Crust #4 (Gluten-Free)

This recipe comes to us from Martha Spinelle.

Celiac.com Sponsor (A12):
My basic gluten-free flour recipe: 2 cups rice flour, ½ cup potato starch, ½ tapioca flour. I substitute this for just about any recipe I come across. Guar/xanthan gum: 1 teaspoon for every cup of gluten-free flour. (I copy the chocolate chip recipe off the package substituting the flour and adding the gum.....this has worked for just about every recipe I have ever found in any cookbook.) May be less for Cakes, and I dont use gum when I make Pancakes.

½ cup tapioca flour
½ cup (1 stick) Margarine
½ cup cornstarch
½ cup butter-flavor Crisco
¼ cup potato starch flour
1 egg, cold
1 cup sweet rice flour
1 tablespoon gluten-free vinegar
1 rounded teaspoon guar gum
4 tablespoons ice water
½ teas salt
Sweet rice flour for rolling
Dash sugar (optional)
(Xanthan gum can be used instead of Guar gum)

Blend together the flours, gum, salt, and sugar. Cut in the cold margarine and Crisco in small dabs until you have shortening the size of lima beans (not cornmeal). Beat the egg using a fork; add the vinegar and ice water. Stir into the flour mixture, forming a ball. You may knead this a bit, since rice flour crusts can stand handling. Refrigerate the dough an hour or more to chill. (I chill mine overnight.)

Divide dough and roll out on a sweet rice-flour board (or on floured plastic wrap, for easier handling). Place in a pie tin. If using plastic wrap, invert the dough into the pan, shape before removing the plastic. Bake as directed for the filling used. For a baked crust, prick the pastry with a fork on sides and bottom. Bake the crust in a preheated 450F oven for 10-12 minutes, or until slightly browned. Cool before filling. Makes enough for a 2-crust 9 pie, + 1 pie shell.