Bash up the biscuits in a bag and melt the butter. Combine the bicuits and melted butter and press down in the base of a spring form tin and chill in the fridge for 10 minutes. Then pour over the tin of dulce de leche and spread evenly. If you are using condensed milk you need to boil the tin for over 2 hours until it becomes toffee. Slice the banana and layer over the toffee and then whip the cream and spread on top. Chill in the fridge for an hour and then EAT IT ALL!