After a lot of testing, here is the way we recommend to hard-boil eggs.
BOIL enough water in a pot to cover your eggs plus one more inch.
PLACE eggs carefully into the boiling water.
COOK 12 minutes (large eggs).
CHILL in cold water or an ice bath for 5 minutes.
That's it! After your eggs have chilled simply place 1/4 cup (or a Negg® capful) of water into the Negg®. Place one hard-boiled egg inside, snap on the cap, and shake 4-12 times so that the egg strikes the top and bottom of the cap. You will feel the shell soften. Then remove the Negg® cap and slide the egg free of its shell.