Do not open sweetened condensed milk cans, but remove the paper on the outside of the cans.
Put water into crock pot, then put UNOPENED sweetened condensed milk cans into water. Turn on low, and allow to simmer overnight, or for 8 hours.
Remove cans from water. Allow to cool, then open cans. Empty contents (should be a rich, caramel color) into a bowl and with a whisk whip until smooth and fluffy. Pour into pie shell, and top with cool whip.