Prepare the Banana Pudding Filling: Whisk the instant banana cream pudding mix with cold milk in a mixing bowl until smooth and thickened. Let it sit for a few minutes, then gently fold in the whipped topping and vanilla extract. Refrigerate the filling while you prepare the Hawaiian rolls.
Prepare the Hawaiian Rolls: Preheat the oven to 350°F. Arrange the Hawaiian rolls on a baking sheet. Using a small paring knife, carefully make an opening in the side of each roll, creating a pocket for the filling without cutting completely through.
Brush With Butter: Melt the butter and lightly brush the outside of each Hawaiian roll. Make sure the rolls are evenly coated without becoming overly saturated.
Toast the Rolls: Place the buttered rolls in the preheated oven and bake for 6–8 minutes, or until the outside is lightly golden and the rolls remain soft in the center.
Add the Banana: Remove the toasted rolls from the oven and let them cool for a few minutes. Slice the bananas into thin pieces and gently place a few slices inside each roll.
Fill With Banana Pudding: Transfer the chilled banana pudding mixture to a piping bag. Carefully pipe the pudding into the opening of each Hawaiian roll, filling the center without overfilling.
Add the Vanilla Wafer Topping: Crush the vanilla wafer cookies into small crumbs. Sprinkle the crumbs over the pudding-filled rolls. Add a small piece of vanilla wafer on top for extra crunch if desired.
Finish and Serve: Lightly dust the finished donuts with powdered sugar. Add an optional banana slice or vanilla wafer for garnish. Serve fresh for the best combination of soft Hawaiian rolls, creamy banana pudding, fresh banana, and cookie crunch.