Wipe out skillet to clean; fill with 2 to 3 inches water. Add vinegar to water. Heat to boiling; reduce to simmering. Break cold eggs, one at a time, into custard cup or saucer. Holding dish close to water’s surface, carefully slip eggs into water. Cook 3 to 5 minutes or until whites and yolks are firm, not runny (water should be gently simmering and not boiling). Remove with slotted spoon.