Place the unopened can of condensed milk in a saucepan over medium heat.
Cover with water and bring to a boil.
Boil gently for 4 to 4 1/2 hours, adding water to the pan when necessary.
Let stand until cool.
Slice the bananas into the pie shell.
Pour the cooled caramelized milk over the bananas.
Top with the whipped topping, sealing to the edge and making swirls with the back of a spoon.
Break the candy bar into pieces and garnish the top of the pie.
Chill, covered, until serving time.