Separate yolks, set aside for meringue. Be SURE you don't get ANY yolk in the whites! The meringue won't come to a peak, or get stiff if you do.
Place all of the pudding ingredients except vanilla and butter in a medium saucepan. Bring to a low boil on medium heat, stirring constantly. When it starts boiling add vanilla and butter. Continue stirring for 3 minutes. Take off heat. Set aside to cool.
While the pudding is cooling, beat egg whites with an electric mixer, adding sugar slowly while mixing. Beat until stiff enough to form peaks. Test by lifting beaters from meringue, if it forms peaks then it is ready.
NOTE: You can substitute whipped topping in place of the meringue, but you'll need to let the pudding cool longer so the whipped topping won't melt. (And you'll omit the broiling, if you use the whipped topping instead of meringue.)
Line an ovenproof dish with vanilla wafers and sliced bananas. Pour about 1/3 of pudding over this. Continue to layer these ingredients until they are all used.
Spread meringue (or whipped topping) over the layers, and form peaks with a spoon by swirling the spoon in the meringue and lifting quickly. Place in oven and broil for about 1 & 1/2 to 2 minutes, or until meringue is slightly browned. OMIT broiling if you use whipped topping. Sprinkle with crushed wafers, if desired, and serve now or cool and serve later. Another one of those - some like it hot, some like it cold things!