These are fun to make and are a sort of crunchy-chewy cookie. Great for entertaining guests or just when you feel like doing something a little different. We enjoyed them because it was something new and different.
Preheat oven to 300 degrees F (150 C or Gas Mark 2) Line 2 baking sheets with parchment paper. Set aside. Place the egg whites in a medium mixing bowl and let stand at room temperature for 30 minutes.
Add vanilla and cream of tartar to egg whites. Beat with an electric mixer on medium speed until soft peaks form and the sugar is almost disolved. Spoon mixture int a piping bag fitted with a large round nozzel. (1/2 inch opening) Pipe about two thirds of meringue mixture into 1 1/2 diameter mounds about 1 inch apart on the prepared baking sheets. With the remaining meringue, pipe 1-inch tall bases about 1/2 inch apart on baking sheets.
Bake for 20-25 minutes, or until meringues just begin to brown. Turn off the oven. Let meringues dry in the oven with the door closed for 30 minutes. Remove meringues from pans and transfer to wire rack to cool.
In a small, heavy saucepan over low heat, melt the chocolate. Spread a scant 1/2 teaspoon of melted chocolon the underside of each mushroom cap. Attach stems inserting top ends in the center of chocolate mixture, pressing gently into the mushroom cap. Let mushrooms dry upside down on racks until chocolate is set. To serve, sift combined confectioners' sugar and cocoa powder over tops of mushrooms.