The look on his face was priceless when he tasted the frosting and was trying so hard to figure out how to nicely tell me it was NOT good! I managed great shock and dismay when he finally said 'there's no sugar in it'. His Mother In Law tasted it and brought up the clue that broke the joke wide open...'is that potatoes??'
Why yes, yes it is! Meatloaf cake layers frosted with mashed potatoes.
I had made another cake though so all is forgiven (I hope) and we were able to trick the kids all into trying the 'frosting'.