In a large mixing bowl, whisk together the whole milk, sweetened condensed milk, and instant vanilla pudding mix until well combined. Let it sit for about 5 minutes to thicken.

In another bowl, beat the heavy whipping cream and vanilla extract until stiff peaks form. Gently fold the whipped cream into the pudding mixture until fully incorporated.

In a 9x13 inch dish, layer half of the Nilla Wafers on the bottom. Top with half of the sliced bananas and half of the pudding mixture. If using, sprinkle half of the mini marshmallows over the pudding.

Repeat the layers with the remaining Nilla Wafers, bananas, pudding mixture, and mini marshmallows.

Finish by sprinkling the crushed Nilla Wafers on top for garnish.

Cover the dish with plastic wrap and refrigerate for at least 4 hours, or overnight for best results. This allows the flavors to meld and the Nilla Wafers to soften.