The Perfect Hardboiled Egg - Hard-boiled eggs can be tricky. If you cook them too long, the yolk turns green. An overcooked yolk is like overcooked asparagus -- nobody wants that! If you don't cook your eggs long enough, then you get a soft-boiled egg (which is delicious, except for when you're aiming for a hard-boiled egg). Our technique results in a perfect hard-boiled egg, every time.