Place the biscuits into a freezer bag and crush using a rolling pin until they resemble breadcrumbs.
Melt the butter in a small saucepan over a low to medium heat.
Mix together the crushed biscuits and melted butter in a bowl until well combined. Spoon the mixture into the bottom of a tart tin and press down to form an even layer.
Spread the dulce de leche evenly over the biscuit base.
Arrange the sliced bananas in an even layer on top of the dulce de leche. Cover the tart tin with cling film and chill in the fridge for one hour.
When the banoffee base has chilled, whip the cream and icing sugar until soft peaks form when the whisk is removed. Spread the whipped cream over the bananas.
Just before serving, sprinkle over the grated chocolate.