I was asked for the recipe I used to make this cake awhile back and I have just now remembered to find it and blog it (sorry rachel!). It seems like a bit of work, especially if you don't have some of the ingredients just laying around like the GF flours or the sunflower seen butter, but it's worth it to go get them.
Now on the frosting, you just add 2/3 cup of sunflower seed butter to it, and I buy pre made vegan marshmallow fluff online but hopefully you can find some where you live.
(if not I think the frosting will live without it, just use less sunflower seed butter.) =)