Place frozen banana chunks in a high-powered blender or food processor and begin to process on low. (It will look grainy.) Turn off machine and use a rubber spatula to scrape down the sides. Continue processing until bananas get creamy and increase in volume, scraping down the sides as necessary. Remove to a bowl. Slowly fold in 1 cup whipped topping and 1/2 cup vanilla wafers. Transfer to 4 dishes and top each with additional whipped topping, vanilla wafers and sliced banana.