Put the eggs in a saucepan and add enough cold water to cover them by about 1 inch. Set the pan over medium-high heat and as soon as the water reaches a brisk simmer, start timing. As the eggs cook, adjust the heat as needed to maintain a brisk simmer. (Though we talk about hard-boiled eggs—and we’re using that term here—the fact is that cooking eggs in boiling water cracks the shell and makes the eggs tough and rubbery. A simmer works much better.)