Preparing the Cupcake Batter:

1. Preheat the oven to 350°F (180°C) and line a muffin tin with cupcake liners.

2. In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

3. In a large mixing bowl, cream the butter and sugar together until light and fluffy.

4. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.

5. Mix in the mashed bananas and sour cream until well combined.

6. Gradually add the dry ingredients to the wet ingredients, alternating with the milk, beginning and ending with the dry ingredients. Mix until just combined.

7. Fill each cupcake liner about 2/3 full with the batter.

8. Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean.

9. Let the cupcakes cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.

Making the Vanilla Pudding:

1. In a medium bowl, whisk together the instant vanilla pudding mix and 1 1/2 cups cold milk until smooth.

2. Refrigerate the pudding for about 5 minutes to set.

Preparing the Whipped Cream:

1. In a mixing bowl, whip the heavy cream until it starts to thicken.

2. Add the powdered sugar and vanilla extract, then continue to whip until stiff peaks form.

Assembling the Cupcakes:

1. Using a cupcake corer or a knife, remove the center of each cupcake to create a well.

2. Fill each well with a spoonful of the prepared vanilla pudding.

3. Transfer the whipped cream to a piping bag fitted with a star tip and pipe a swirl of whipped cream on top of each cupcake.

4. Garnish each cupcake with a vanilla wafer cookie.

5. Refrigerate the cupcakes until ready to serve.