In a large, covered pot, boil can of unopened sweetened condensed milk for 4 hours (yep, you read that right - 4 hours).
The can must be completely submerged in water the entire time.
Allow the can to cool completely before use.
For the whipped cream topping:
In a medium bowl, with an electric mixer, whisk heavy cream, powdered sugar and vanilla together until stiff peaks form.
Once can of sweetened condensed milk can (toffee) has cooled, spread the toffee filling into the graham cracker crust.
Slice bananas and layer on top of the filling.
Spread whipped cream on top of bananas and sprinkle with chocolate shavings or chocolate sprinkles. Keep pie refrigerated.
This is a pretty rich dessert so serve in relatively small slices. Also, I've been told that the cans of Dulce De Leche make a good substitute for boiling cans of sweetened condensed milk. Short on time or energy? Use COOL WHIP instead of the homemade whipped cream.