In the bowl of a stand mixer fitted with the whisk attachment mix the sweetened condensed milk and cold water until combined. Add the pudding mix and mix on medium speed for 2 minutes. Transfer the mixture to a bowl, cover, and refrigerate for 3-4 hours or overnight.
Remove pudding mixture from the fridge, it should be cold and firm
In the bowl of your stand mixer (with whisk attachment) or with hand beaters, beat the whipping cream until stiff peaks form.
Using a rubber spatula, fold half of the pudding mixture into the whipped cream. Once almost combined, add the remaining pudding mixture and fold until combined.
Slice the bananas.
To your serving dish (you can use a trifle, or individual glass jars) add a handful of the Nilla wafer chunks to the bottom of the dish, then top with sliced bananas, and then a layer of pudding. Repeat with cookies, bananas, and pudding. Depending on the dish you’re using you can do another layer of cookies, bananas, pudding.