Place the chocolate in a small saucepan with the milk, Tia Maria or Brandy and coffee, and gently melt everything together to create a sauce. Once smooth, leave to cool slightly to thicken.
In 2 sundae glasses, glass dishes or one large bowl to share, layer up the sliced banana, scoops of ice-cream, crumbled biscuits and mocha sauce. Scatter with the chopped hazelnuts and serve straight away.
