In a large bowl, beat together the sweetened condensed milk and 1 ½ cups ice cold water until well combined - about 1 minute. Add the pudding mix and beat well - about 2 minutes. Cover and refrigerate for 3-4 hours or overnight.

In another large bowl, whip the 3 cups heavy cream until stiff peaks form. Gently fold the whipped cream into the pudding mixture until no streaks of pudding remain.

To assemble dessert, arrange ⅓ of the Nilla wafers covering the bottom, overlapping if necessary. Next, layer ⅓ of the bananas, and ⅓ of the pudding mixture. Repeat twice more, garnishing with additional wafers or wafer crumbs on the top layer.

Cover tightly and allow to chill in the fridge for at least 4 hours - or up to 8 hours, no longer to prevent bananas from browning.