_For hard-cooked eggs_, bring water to simmering and simmer 20 to 25
minutes. Do not let the water boil. Serve the eggs hot or plunge them
at once into cold running water and leave until cold.
NOTE: The green discoloration that sometimes appears between the white
and the yolk of a hard-cooked egg results from a chemical reaction,
which is harmless. To help prevent this discoloration, cook eggs at low
temperature, avoid overcooking, and cool promptly.