Preheat your oven to 325°F (165°C). In a mixing bowl, combine crushed vanilla wafer cookies, granulated sugar, and optional cinnamon with melted unsalted butter. Mix until well combined, then press this mixture firmly into the bottom and up the sides of a springform pan. Bake the crust for 10 minutes until it's firm to the touch and set, then remove from the oven to cool.

In a large mixing bowl, beat softened cream cheese using an electric mixer until smooth and creamy. Gradually add in granulated sugar, mixing until fully incorporated. Add eggs one at a time, blending thoroughly after each addition. Gently fold in vanilla extract, sour cream, instant banana pudding mix, and mashed ripe bananas until just combined.

Pour the cheesecake filling into the cooled crust, smoothing the top with a spatula. Place the springform pan inside a larger baking dish and fill it with hot water, creating a water bath. Carefully transfer to the preheated oven and bake for 60-65 minutes until the edges appear set but the center has a slight jiggle.

While the cheesecake cools, prepare the crunchy topping. In a mixing bowl, combine crushed vanilla wafers, melted butter, brown sugar, and a sprinkle of cinnamon. Spread this mixture on a baking sheet and bake it for 8-10 minutes until golden brown. Let the topping cool.

Once the cheesecake has chilled completely, remove it from the springform pan carefully. Sprinkle the crunchy topping over the cheesecake. For presentation, garnish with fresh banana slices, whipped cream, and caramel sauce if desired.