Preheat your oven to 350°F. Line 24 muffin tins with paper liners and place one vanilla wafer, flat side down, in each cup.

In a large bowl, mix the cake mix, mashed bananas, milk, eggs, oil, and vanilla extract. Stir until fully combined.

Fill each cup about two-thirds full of batter. Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Let cupcakes cool for 5 minutes in the pan, then transfer to a wire rack to cool completely.

While cupcakes cool, prepare the filling. In a saucepan, whisk together milk and pudding mix. Cook over medium heat, stirring continuously, until the pudding thickens enough to coat the back of a spoon.

Remove filling from heat and stir in butter and vanilla extract. Pour into a small bowl, press plastic wrap directly onto the surface to prevent skin from forming, and chill until completely cool.

For the whipped cream, beat heavy cream in a medium bowl until it starts to thicken. Add sugar and continue beating until stiff peaks form.

Use an apple corer or teaspoon to hollow out the center of each cupcake. Fill a piping bag with the chilled pudding and fill the cupcakes. Top each one with whipped cream and sprinkle crushed vanilla wafers on top, if desired. Serve immediately or refrigerate leftovers.