Preheat the oven: Preheat your oven to 350°F (175°C). Line a 12-cup muffin tin with cupcake liners.

1. Mix the dry ingredients: In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
2. Cream the butter and sugars: In a large bowl, cream together the softened butter, granulated sugar, and brown sugar using an electric mixer on medium speed until light and fluffy, about 3-4 minutes.
3. Add eggs and vanilla: Beat in the eggs, one at a time, ensuring each is well combined. Stir in the vanilla extract.
4. Add the dry ingredients and buttermilk: Gradually add the dry ingredients to the wet mixture in 3 parts, alternating with the buttermilk in 2 parts. Begin and end with the dry ingredients. Mix until just combined.
5. Add the bananas: Gently fold in the mashed bananas, being careful not to overmix.
6. Bake the cupcakes: Divide the batter evenly among the 12 cupcake liners, filling each about 2/3 full. Bake for 18-20 minutes, or until a toothpick inserted into the center of the cupcakes comes out clean. Let the cupcakes cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.
7. Make the vanilla pudding filling: In a medium bowl, whisk together the instant vanilla pudding mix and cold milk. Whisk until the pudding thickens, about 2 minutes. Let it sit for 5 minutes to firm up.
8. Make the whipped cream topping: In a chilled bowl, beat the heavy cream with powdered sugar and vanilla extract using an electric mixer on medium-high speed until stiff peaks form.
9. Assemble the cupcakes: Once the cupcakes are completely cooled, use a small knife or cupcake corer to remove the center of each cupcake, leaving a small well in the middle. Spoon or pipe a generous amount of vanilla pudding into the center of each cupcake. Dollop or pipe a swirl of whipped cream on top of each cupcake. Garnish with a slice of banana and a Nilla wafer cookie, if desired.
10. Serve: These cupcakes are now ready to serve! They’re perfect for a sweet treat any time of year, especially when you’re craving something reminiscent of banana pudding.