Crumble the vanilla wafers into roughly 1/2-inch pieces and set aside in a bowl. Slice the bananas into 1/4-inch rounds and place them in a separate bowl—I like to toss them with a tiny splash of lemon juice if you have it on hand to prevent browning, though it's optional. Measure out the milk, whipped topping, and marshmallows so everything is ready to go when you need it.

Pour the instant banana pudding mix into a large mixing bowl and add the milk. Whisk together vigorously for about 2 minutes until the mixture is smooth and combined. Let the pudding sit undisturbed for 3 minutes—this allows the pudding to thicken properly and achieve the right consistency for folding in the other ingredients.

Once the pudding has set, gently fold in the whipped topping using a spatula until mostly combined—don't overmix or you'll deflate the fluffiness. Then fold in the marshmallows, crumbled vanilla wafers from Step 1, and sliced bananas from Step 1. I always add the bananas last and fold them in gently to keep them intact and prevent them from breaking apart. Add the vanilla extract and give everything one final gentle fold to incorporate. Transfer to a serving bowl or individual cups and chill until ready to serve.