Heat the oven to 350°F. Line two 12-cup muffin tins with paper liners, placing one vanilla wafer in the bottom of each liner if desired.

Whisk the cake mix and one package of instant banana pudding mix together in a large bowl. Add the eggs, vegetable oil, whole milk, mashed bananas, and vanilla extract, then beat just until the batter is smooth.

Divide the batter among the liners, filling each about two-thirds full. Bake for 18–22 minutes, until the tops spring back lightly and a toothpick inserted in the center comes out clean or with a few moist crumbs.

Cool the cupcakes in the pans for about 5 minutes, then transfer them to a wire rack and cool completely before filling or frosting.

Whisk the second package of instant banana pudding mix with 2 cups cold whole milk for about 2 minutes. Let it stand for 5 minutes to thicken, then fold in 1 cup whipped topping if you prefer a lighter filling.

Cut a small cone from the center of each cooled cupcake or use a cupcake corer. Fill each cavity with banana pudding and replace the tops if desired.

Beat the cold heavy cream, powdered sugar, and vanilla extract until stiff peaks form. Pipe or spoon the whipped cream over each cupcake.

Decorate with a vanilla wafer and, just before serving, a thin banana slice or crushed vanilla wafers. Refrigerate the cupcakes until ready to serve.