Prepare the CrustPreheat oven to 325°F (163°C). Mix crushed Nilla Wafers, melted butter, and sugar in a bowl until combined and the texture resembles wet sand. Press into the bottom of a 9-inch springform pan. Bake for 10 minutes and cool completely.
Make the FillingIn a large bowl, beat softened cream cheese and granulated sugar until smooth and fluffy. Add eggs one at a time, mixing well after each. Stir in mashed bananas, sour cream, vanilla extract, and salt. Mix until fully combined.
Bake the CheesecakePour the cheesecake filling over the cooled crust. Wrap the bottom of the pan with foil and place into a larger roasting pan. Pour hot water into the roasting pan until it reaches halfway up the sides of the springform pan. Bake for 1 hour to 1 hour and 10 minutes, or until the center is set but slightly jiggly. Turn off the oven, crack the door, and let cool in the oven for 1 hour.
ChillRemove from the oven and refrigerate for at least 4 hours or overnight.
Make the Whipped ToppingBeat heavy cream, powdered sugar, and vanilla extract in a large bowl until stiff peaks form. Spread or pipe onto chilled cheesecake.
Garnish and ServeTop with banana slices and crushed Nilla Wafers just before serving.