Mix the pudding mix and milk at a low speed until it's thick.
Blend in the sour cream and half of the Cool Whip.
In a trifle bowl or other large bowl, spread ⅓ of the pudding in an even layer. Add a layer of vanilla wafers, then top with ½ of the banana slices. Repeat with another pudding-wafer-banana mixture.
Top with the remaining pudding, then spread the rest of the whipped topping on top. Sprinkle on crushed vanilla wafers.
Cover and refrigerate for at least 3 hours before serving.
Notes
Use ripe but firm bananas so they add sweetness without turning mushy.
Always let the frozen whipped topping fully thaw so it folds easily into the pudding mixture.
If you're worried about the banana slices turning brown in the pudding, toss them lightly in lemon juice, club soda, or soda water to help prevent oxidation.
For a light and airy pudding mixture, fold the whipped topping gently to avoid deflating it.
Store leftovers covered tightly in plastic wrap in the fridge for up to 4 days.
This nutrition information is based on the exact products I used in this recipe. Brands and sizes of products could alter exact nutrition and should always be calculated independently.