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Thank you all for help.  I was looking for a way to make frosting without
using the confectionary sugar, since I am gluten, soy, corn and dairy
sensitive.  Here are some of the suggestions.

Use a blender and put granulated sugar in it and blend until the sugar turns
to powder.  Others suggested that one use tapioca starch or arrowroot in the
mix to replace the cornstarch. Another suggestion was to use a coffee
grinder. I have tried using a food processor to grind the sugar into powder,
but it did not get fine enough.  I will try a blender, or locate someone with
a coffee grinder.

I have not tried it yet, but thank everyone for their help.