RE: Baking Powder Substitute
This may be too late for the original poster but Hain Baking Powder is corn free, I believe. I have used it in the past for a corn free, gluten free, dairy free, egg free cake. I made the same cake with Frontier brand baking powder (contains corn) and I could not tell a noticeable difference.
As for the cake recipe itself, I had some struggles with it. This mixture was so thick, it was impossible to pour into cake pans. I had to add much more liquid for some reason. It tasted really good the day of but by the next day, it wasn't as tasty. I think it is a solid recipe though and will be working with it more!