Place the pudding mix into a 4-quart bowl and set aside.

In a 2-quart liquid measuring cup or bowl with a spout, whisk together the sweetened condensed milk and water until smooth.

Slowly pour the liquid into the bowl with the pudding mix while whisking constantly until thoroughly combined. Scrape the bottom and sides of the bowl with a spatula and stir until smooth. Cover with plastic wrap and place in the refrigerator for a minimum of 30 minutes. The pudding can be made ahead up to 24 hours.

In a stand mixer fitted with the whisk, whip the heavy cream on medium speed for 1 minute, until the cream starts to thicken, then increase the speed to medium-high and whip until stiff peaks form. Be careful not to overwhip.

With the mixer running on low speed, add the pudding mixture a spoonful at a time. Mix until well blended and no streaks of pudding remain. Scrape the bottom and sides of the bowl.

To assemble: Select either a trifle bowl, a 9x13-inch pan, or a wide glass bowl with a 4- to 5-quart capacity, or individual bowls.

If using a trifle bowl, spread one-quarter of the pudding over the bottom of the bowl, then layer with one-third of the cookies and enough banana slices to cover the cookie layer. Repeat the layering twice more. End with a final layer of pudding. Garnish the top with additional vanilla wafer cookies or cookie crumbs.

Cover tightly with plastic wrap and refrigerate for 4 to 6 hours. The cookies should be tender when poked with a knife. This dessert is best served within 12 hours of assembling.