After a few experiments and a cracked egg or two, I've figured out exactly how long to boil an egg to get it perfectly hard-boiled (to my taste anyway). First bring the water to a rolling boil, meaning a vigorous state of boiling.

Then gently drop the egg into the boiling water using a spoon or a spatula. Try not to crack the egg when you drop it in the water. Start a timer and remove the egg exactly 9 minutes later. Run it under cold water, and voila! You've got yourself a perfect hard boiled egg.