from: Allergen-Free Baker's Handbook
4 cups superfine brown rice flour (Authentic Foods superfine brown rice flour is suggested)
1 1/3 cups potato starch (not potato flour)
2/3 cup tapioca flour (also called tapioca starch)
1. To measure flour, use a large spoon to scoop the flour into the measuring cup, then level it off with the back of a knife or straight edge. Do not use the measuring cup itself to scoop your flour when measuring! It will compact the flour and you will wind up with too much for the recipe.
2. Combine all ingredients in a gallon-size zipper-top bag. Shake until well blended. Store in the refrigerator until ready to use.