I must share with you this that my daughter (10) concocted up today. She wanted the two pound seventy-nine tub of ready chocolate creamy icing. No way, I says, and so we looked at the ingredients and she decided to make her own.
Icing sugar, cocoa powder and veg oil made a fantastic mix - just like the real thing - you can spread it on thick and it stays moist. Just play with the quantities until it seems and tastes right. Like the chocolate fudge cake filling and topping. We did play with butter icing and add cocoa but that was far too sickly and just felt wrong.
The mix sounds foul but tastes amazing. Try it!