Corn free Baking powder substitute
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The corn starch contained in Baking Powder is just a filler. So you can omit that from a homemade recipe and it will still work just fine. So you would use 1 part baking soda to 2 parts cream of tartar to make your own recipe. Be sure to mix it very well using a sifter to get all of the lumps out. Store in an airtight container to prevent absorbing odors and moisture. See: http://www.marthastewart.com/967961/scott-peacocks-homemade-baking-powder