1/2cuparrowroot powderaround $5/pound in natural food stores by the rest of the flours! I imagine tapioca or potato starch could work too. This is to help with binding of the frosting without adding more powdered sugar
1cuppowdered sugarWhole Foods Brand and Safeway's O Organics are corn free, you could add more if you like it sweeter, but me and the kids loved this as is)
Preheat oven to 350 degrees and grease 2 9" cake pans. You could certainly do this is any shape you wanted: bundt, rectangle, etc.
In a mixer, beat the prune puree, oil, honey, sugar, vinegar, and vanilla.
With the mixer running, sprinkle in the salt, soda, and guar gum.
Continue with the cocoa, tapioca and brown rice flours. Batter should look like a typical cake batter.
Pour into prepared pans.
Bake for about 25-30 minutes until knife inserted in center comes out clean.
Let it cool a couple of minutes, and invert the cakes on a wire rack to cool completely.
Frost when cool (If you are doing a more fancy frosting job, freezing the cake first makes it easier to work with!