Preheat the oven to 350 degrees F (175 degrees C). Lightly grease a 9x13-inch baking dish with cooking spray.
Whisk pudding mix and milk together in a large bowl until thickened, 2 to 3 minutes. Gently mix sliced bananas into the thickened pudding; set aside.
Arrange vanilla wafers in an even layer in the bottom of the prepared baking dish. Spread pudding and banana mixture evenly over wafers.
Sprinkle cake mix evenly over pudding mixture. Arrange sliced butter evenly over the cake mix.
Bake in the preheated oven until the top is golden brown and the filling is bubbly, 45 to 55 minutes. Remove from the oven and cool on a wire rack for 30 minutes. Refrigerate until chilled, at least 2 hours.
Beat cream, sugar, and vanilla together in a medium bowl with an electric mixer until stiff peaks form.
Spread whipped cream over the chilled cake. Garnish with additional crushed vanilla wafers and fresh sliced bananas before serving. Recipe developed by Jaelyn Luong
