2 egg whites
1/2 cup sugar
unsweetened cocoa powder or ground chocolate
leftover frosting or melted chocolate
Preheat the oven to the lowest setting possible (150 or 200).
Line a cookie sheet with parchment paper.
In a big bowl, beat the egg whites until soft peaks form. Beat in the sugar gradually until stiff peaks form.
Put the meringue mixture into a pastry bag (or ziplock).
For the mushroom tops, pipe flat circles onto the cookie sheet. Pull the pastry bag off to the side to avoid making peaks on the top of the mushroom caps. For the stems, pipe a small amount of meringue straight up, so it looks like an elongated kiss. Vary the sizes of the caps and stems to make the mushrooms look more random and natural.
Dust a tiny amount of cocoa onto the caps only to make them spotted.
Put the caps in the oven for about 2 hours or until they seem thoroughly dry. Turn the oven off and leave the meringues in the oven for a few more hours.
When the meringues are cool, remove them from the parchment.
Drill a small hole in the base of the caps with a butter knife. Fill the whole with frosting or melted chocolate, then stick in a mushroom stem. It should stand up by itself.