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Hi,

I have found that if you substitute plain rice, potato, soy flour, etc. you
need some amount of Xanthan gum to keep it together.

I have had great luck using Welplan or EnerG baking mix as a straight
substitute. No Xanthan gum needed and things come out just right.  Even corn
bread which is hard to keep from crumbling.  Health Food stores also sell
Gluten-free baking mixes.  They are usually a combination of rice
flours/starches and potato or soy.

Good luck!