I am pretty sure they will sit ok on any type of icing. I have used them ontop of fondant, royal icing and buttercream. To make a buttercream, i just beat up the butter and pure icing sugar until the mixture is thickened to my liking. Generally i think the rule is about double the weight of icing sugar to butter, but dont quote me on that, as I just keep adding. Then you can add whatever flavouring you want to it and colours.
