Hi could anyone tell me what would be the easiest butter cream would be for crumb coating? At the moment I use the basic icing sugar with butter but it doesn't seem to harden and is still soft when I apply the fondant sometimes leaving me with bumpy cakes

Crusting is caused by evaporation in a recipe which contains fat, a small amount of liquid and which is heavy on powdered sugar (your basic American b/c recipe).

Since you didn't post your recipe, I can only offer that you probably need more powdered sugar.

HTH

ok thanks, I dont have a reciepe as such, just mix butter with icing sugar until it tastes nice! lol I will try using a full fat butter and more icing sugar