Step 1: In a large bowl, whisk together the sweetened condensed milk and ice-cold water until thoroughly combined.
Step 2: Add the instant vanilla pudding mix to the milk mixture. Whisk vigorously for about 2 minutes until no lumps remain and the mixture is smooth.
Step 3: Cover the bowl tightly with plastic wrap and refrigerate for at least 4 hours, or ideally overnight, until the pudding is firm and set.
Step 4: In a separate large chilled bowl, whip the heavy cream using a hand mixer or stand mixer until stiff peaks form. Be careful not to over-beat into butter.
Step 5: Gently fold the chilled pudding mixture into the whipped cream using a rubber spatula. Use a slow ‘under-and-over’ motion to maintain the airiness until the color is uniform.
Step 6: In a large trifle bowl or glass dish, create the first layer by covering the bottom with one-third of the Nilla wafers.
Step 7: Add a layer of one-third of the sliced bananas over the wafers.
Step 8: Spread one-third of the pudding mixture over the bananas, smoothing it out to the edges.
Step 9: Repeat the layers (wafers, bananas, pudding) two more times. For the final layer, you can crumble a few extra wafers on top for decoration.
Step 10: Cover with plastic wrap and refrigerate for at least 4 to 8 hours before serving. This allows the wafers to soften to a cake-like texture.