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Scott,
The proportions of Betty Hagman's GF flour mixture is 2 parts white rice
flour, 2/3 parts potato starch flour, and 1/3 part tapioca starch. I
usually up the measurements by a factor of three so that it comes outs to
6 cups, 2 cups and 1 cup respectively. I put this in a flour canister,
mix it well and use as needed.
Ellen Eagan
eagan@ pangloss.ucsf.edu