In a large mixing bowl, whisk together the cold milk and the two packages of instant vanilla pudding mix. Continue whisking for about two minutes until the mixture begins to thicken. Stir in the sweetened condensed milk and vanilla extract until the mixture is smooth and well combined.
Gently fold in about half of the whipped topping (or homemade whipped cream) into the pudding mixture. Use a spatula to turn the mixture over on itself until no white streaks remain. This makes the pudding light, airy, and extra creamy.
In a large glass trifle bowl, place a single layer of vanilla wafer cookies at the bottom. You can also stand some cookies up against the side of the glass for a pretty visual effect. Top the cookies with a layer of sliced bananas.
Spread about one-third of the pudding mixture over the banana layer, ensuring it reaches the edges of the bowl to seal the layers. Smooth it out with the back of a spoon or an offset spatula.
Repeat the layering process—cookies, bananas, then pudding—until you reach the top of the bowl or run out of ingredients. Usually, you can achieve three full layers in a standard trifle dish.
Spread the remaining whipped topping over the final layer of pudding. Garnish with a few crushed vanilla wafers or a few whole cookies. Cover the bowl with plastic wrap and refrigerate for at least 2 to 4 hours before serving to allow the cookies to soften.