Place the condensed milk in a saucepan. Dissolve the cornflour in 800ml milk and mix with the condensed milk. Add the vanilla and cook over medium heat, stirring constantly, until thickened.
Add the diced dark chocolate and stir until the chocolate melts. Remove from heat, add the cream, stir and let cool slightly.
Dip the wafers in the milk and place in a layer in a serving dish. Cover with a layer of chocolate cream. Make alternate layers of wafers and cream, ending with cream.
Sprinkle over the grated chocolate and refrigerate 4 hours before serving.