Ice the biscuits to your liking (you could use melted 85-90% dark chocolate instead, or leave un-iced if you prefer) and allow it to set before serving.
You could also use the icing simply as "glue" for things like fruit, nuts or chocolate chips/cacao nibs. Alternatively, you could use melted chocolate to decorate.
*You can use a shop-bought blend, but I like using this one.