Prepare the Crust:

1. Preheat the oven to 325°F (160°C), or 140°C for a fan oven.

2. In a food processor, crush the Nilla wafers into fine crumbs. Reserve ½ cup of crumbs for garnish.

3. In a bowl, mix 2 cups of cookie crumbs with the melted butter until evenly moistened.

4. Press the mixture firmly into the bottom and halfway up the sides of a 9-inch springform pan. Set aside.

Make the Cheesecake:

1. In a stand mixer, beat the cream cheese and sugar on high speed until smooth.

2. Add the vanilla extract, then mix in the eggs one at a time, beating just until incorporated.

3. Add the sour cream and mix until smooth. Gently fold in the mashed bananas.

4. Pour the cheesecake batter into the prepared crust.

5. Wrap the outside of the springform pan tightly with two layers of foil to prevent water from seeping in.

6. Place the springform pan into a large roasting pan. Pour boiling water into the roasting pan until it reaches halfway up the sides of the springform pan.

7. Bake for 50-60 minutes, or until the edges are set and the center is slightly wobbly.

8. Turn off the oven, crack the oven door open, and let the cheesecake cool for 1 hour inside the oven. Remove from the water bath and let it cool completely to room temperature.

Make the Banana Pudding:

1. In a medium saucepan, whisk together the sugar, flour, and salt.

2. Add the eggs and whisk until smooth. Gradually add the milk and heavy cream, whisking constantly.

3. Cook over medium heat, stirring continuously until the mixture thickens and comes to a gentle boil.

4. Remove from heat and stir in the butter and vanilla extract. Let the pudding cool for 15 minutes.

Assemble and Chill:

1. Slice 1-2 bananas and arrange them in a single layer over the cooled cheesecake.

2. Spread the banana pudding evenly over the bananas.

3. Refrigerate the cheesecake for at least 4 hours, or overnight, to allow the flavors to meld and set.