Preheat the oven to 350 degrees and line two 12 cup muffin tins with liners. [Depending on how full you fill your cupcakes before baking, you'll have 18-24 cupcakes total] Prepare the cake mix per the instructions on the box except use buttermilk in place of the water. Use the same quantity of eggs and oil called for on the package. By replacing the water with buttermilk it will give the cupcakes a richer flavor. Bake according to the directions then set aside and allow the cupcakes to cool completely before filling.
While the cupcakes are baking, prepare the filling. In a medium size mixing bowl, whip together the softened cream cheese and the sweetened condensed milk for about 2-3 minutes or until fluffy. Next, add 3/4 cup of whole milk, one teaspoon of vanilla extract and the entire box of vanilla pudding. Whip the ingredients together on medium-high speed for 3-4 minutes until the mixture thickens. Fold in one cup of thawed whipped topping by hand. Cut three bananas in half lengthwise, and then cut each in half again. Cut the banana quarters into 1/3-1/2 inch chunks. Using a spatula fold the chopped bananas into the custard filling.
Using a sharp knife, cut the middle out of each cupcake leaving a 1/2 inch border around the edge. The centers are treats for the baker! When removing the centers of the cupcakes, be careful not to cut all the way to the bottom of the cupcake shell. Sprinkle half of the crushed vanilla wafer crumbs into the bottom of the cupcakes, reserving the other half for garnishing the tops. Fill the cupcakes evenly with the custard filling. To finish, pipe the cupcakes with a dollop of whipped topping and sprinkle the tops with the remaining crushed vanilla wafers. Chill thoroughly before serving. Yield: 18-24 filled cupcakes