A chocolate orange sultana cake

Hi,
I really want to make a chocolate orange sultana cake.

I've tried making it with just putting coco powder in the cake mix to make it look brown and chocolatey and also added orange essence and sultana's.
Once cooked I than covered it in melted chocolate with a little more orange essence.

However the cake mixture turned out horrible.

Does anyone have any suggestions or a recipe I could try out.
Thanks very much.