
Start by combining the condensed milk and ice cold water in a medium bowl. Whisk to combine. Then add the vanilla pudding and whisk until well combined. You can do this using a whisk or a stand mixer. Cover with plastic wrap and refrigerate for 3 to 4 hours, until scoop-able with a spoon.
When the vanilla pudding is ready, use a stand mixer or hand mixer to beat whip the heavy cream until stiff peaks form. Gently fold the whipped cream into the pudding mixture until they are well incoroporated.
Peel and slice the bananas into circles. In an 8x12 inch casserole dish (see notes) that is at least 2 inches deep, add a thin layer of the cream. Then add a layer of the vanilla wafers, placing them side by side. Top with a layer of bananas. Repeat the cream layer, then wafers, then bananas. The top layer should be cream.
Crumble any leftover wafer pieces over the top, then cover with plastic wrap and refrigerate for at least 7 hours, or ideally 12 hours. I found that anything less than 7 hours and the wafers are not very soft. Anything more than 10-12 hours and the bananas may brown a little bit, but to be honest, it doesn't show much and it still tastes delicious. Do not place any bananas on top until you are ready to serve. The bananas nestled in the cream will stay fresh longer since they are not exposed to air.
To serve, chop up more bananas and place on top. Scoop the pudding into individual bowls and serve.