Using a stand mixer with whisk attachment, combine sweetened condensed milk and ice cold water on medium speed until well blended, approximately 1 minute. Add instant vanilla pudding mix and beat until completely smooth with no lumps, about 2 minutes more. Transfer to a bowl, cover, and refrigerate until firm, at least 1 hour or overnight.

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

With mixer running on low speed, add the chilled pudding mixture one spoonful at a time to the whipped cream. Mix until well combined with no streaks of pudding remaining.

In a trifle bowl or wide glass bowl, reserve 6-8 cookies for garnish. Spread one-quarter of pudding mixture on bottom. Layer with one-third of cookies and one-third of sliced bananas. Repeat layering process twice more, ending with final layer of pudding mixture.

Garnish top with remaining cookies or cookie crumbs. Cover tightly with plastic wrap and refrigerate 4-6 hours until cookies are tender when poked with knife. Best served within 12 hours of assembly.