In a large mixing bowl, gradually whisk milk into instant pudding mix until you have a creamy pudding. No electric mixer is needed. Stir in the sour cream. Using a whisk, stir the whipped topping into the pudding mixture until it's mostly combined. Continue folding it in with a rubber spatula until all of the whipped topping is combined.
Spread ⅓ of the pudding mixture into a 13x9 pan (or trifle dish). Add a layer of vanilla wafers on top of the pudding. Then add half of the fresh banana slices. Repeat process. Then finish with one more layer of pudding mixture and crumbled cookies on top. Place more crisp vanilla wafers around the edges.
Store covered in refrigerator for up to 3 days. Dessert is best served in the first 24 hours as the bananas will start to turn brown after that, although they will still be safe to eat for another few days.
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Notes
Use fresh Bananas - Perfectly ripe bananas is the key. Your bananas should be very yellow. Not green or with too many brown spots.Whipped Topping - Use frozen whipped topping that has been thawed such as Cool Whip topping. Keep in refrigerator until ready to use. If you prefer, you can make homemade whipped cream. Beat 16 ounces of heavy cream with ¼ cup of sugar until stiff peaks form.