Place milk and pudding mix in a large bowl; beat with a whisk for 2 minutes. Whisk in condensed milk until smooth.
Stir in vanilla, then fold in whipped topping.
Arrange a layer of wafers in the bottom of a glass serving bowl. Top with a layer of banana slices, then a layer of pudding mixture; repeat layers until all ingredients are used.
For best results, chill pudding in the refrigerator for at least 1 hour before serving. Top with extra crushed wafers just before serving.