For best results, use fresh, room-temperature egg whites. The proteins in old egg whites may not dry out properly in the oven. To protect the integrity of the meringue, make sure your bowl and beaters are clean and dry.
Chef’s touch: Use a star tip to pipe decoratively into mounds.
Variation: Vanilla Meringue Cookies: Omit espresso powder and replace with 1 tsp. vanilla extract.