Melt the butter, syrup and chocolate in a pan over a low heat. Stir to make sure all the ingredients are well mixed together. Allow to cool a little before stirring through the biscuits, maltesers and marshmallows and stir well to combine evenly.
Once the cake has almost set, make the glaze. Melt the chocolate and butter in a small pot, when melted, remove from the heat, whisk in the icing sugar and the cream.