Pre-heat your oven to 180°c (or 160°c for a fan assisted oven) and line a couple of baking trays with greaseproof paper.
Cream your butter & sugar on a medium speed until light & fluffy.
Add the egg and mix until combined then sift in the flour and mix to form a dough.
Roll the dough on a floured surface to around 1cm thick. Using a round cutter, cut your biscuits & transfer to your baking tray.
Bake for around 10 minutes until the edges of the biscuit are just golden.
When still warm but cool enough to touch, add the jam to the under side of half your biscuits and pop the other half on top of these to sandwich together.
When completely cool, make your icing by mixing icing sugar & gradually adding the boiling water until you're happy with the consistency - "gloopy" is a great way to describe it! Gently dip the top of your biscuits into the icing to cover and top with your decoration of choice!