Martha Stewart and Simply Recipes recommend 12 minutes for perfect hard boiled eggs. Arrange 12 large eggs in a single layer and add cool water measuring about an inch above the eggs. Heat just to boiling, cover and set aside for 12 minutes.
Adjust the standing in hot water time to nine minutes for medium eggs or 15 minutes for extra large eggs. Drain and serve the eggs warm or cool them in cold running water or in ice water to stop the cooking process. Once cooled, the eggs can be used immediately or stored in the refrigerator for up to three days. Start with room temperature eggs and experiment with timing to make a perfect hard boiled egg.