In a large bowl, whisk together the sweetened condensed milk and ice‑cold water until fully combined (about 1 minute) :contentReference[oaicite:0]{index=0}

Add the instant vanilla pudding mix and whisk until smooth, with no lumps (about 2 minutes) :contentReference[oaicite:1]{index=1}

Cover the pudding mixture and refrigerate until firm (at least 1 hour, preferably 3–4 hours or overnight) :contentReference[oaicite:2]{index=2}

In another bowl, whip the heavy cream (and optional splash of vanilla) until stiff peaks form. Be careful not to overwhip. :contentReference[oaicite:3]{index=3}

Gently fold the whipped cream into the set pudding mixture until fully combined and no streaks remain. :contentReference[oaicite:4]{index=4}

To assemble, choose a trifle bowl or wide glass serving dish. Begin with a layer of pudding, then a layer of vanilla wafers, then a layer of banana slices. Repeat layering (approximately 3 layers), ending with a top layer of pudding. Garnish with reserved wafers or wafer crumbs. :contentReference[oaicite:5]{index=5}

Cover tightly and refrigerate for at least 4 hours (up to 8 or more, but bananas may brown) before serving :contentReference[oaicite:6]{index=6}