Les - your Fairy Cake describes what I would call a Butterfly Bun with one small missing ingredient. You have missed out the small dollop of jam put into the excavated hole before filling with buttercream and placing the butterfly's wings on top.

"Crumpets were what toffee-nosed public school kids toasted in front of an open fire. "
I thought that was Tom Brown?

Quack!
GtD.