Welcome to DC KrazyKat! I don't know what a hostess cup cake is to even begin to help you! Could the icing be either butter or glace icings? (Just a stab in the dark.)
OH not from USA huh ........well its hard and flat but when u bite into it , it cracks i don't think there's any butter its like whats on a maple bar if you know what those are or a chocolate bar or doughnut
I think over here they use a (commercial) thick glace icing on donuts which is just icing sugar (powdered sugar, not granulated) and water with your choice of any colourings or flavourings. Don't know what a Maple bar is and a chocolate bar to me is just coated in chocolate!! I guess a fondant icing is possible but not sure.
There are heaps and heaps of bakers on this site so one will no doubt be along shortly and steer you better than I can.
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