-4 egg whites, preferably room temperature
-1 cup super-fine sugar (if needed, you can just beat regular granulated sugar in the blender for 30 seconds. Superfine is NOT the same thing as powdered sugar, which you should not use.)
-1 tsp vanilla extract
-1/2 tsp cream of tartar OR meringue powder
-small amount cocoa powder for dusting/coloring mushroom caps (optional)
-1 bag semi-sweet chocolate chips (not milk chocolate)
Preheat oven to 375 degrees. Cover two cookie sheets with parchment paper or (very lightly) sprayed aluminum foil, shiny-side-down. In a mixing bowl, combine 4 room temperature egg whites with 1 cup superfine white sugar (or just run regular granulated through a blender for thirty seconds before adding to egg).
In an electric mixer, beat the mixture on HIGH speed for one minute, or until well-mixed. Add 1 tsp vanilla extract and about 1/2 tsp cream of tartar or meringue powder and return to HIGH speed. Beat several minutes, until meringue forms very stiff peaks.
As you’re checking this periodically, a good rule is that if you stop the beater, the mixture should stay in that rippled-mound form for at least 30 seconds after the beater stops moving. Or, you can use a spoon to pick up a bit of meringue and drop it onto the surface of the mixture. If it keeps its stiff upright shape for more than a few seconds, it’s ready to go.
(Alternately, a spoon should also be able to stand erect in the mixture without slipping or falling over.)
When the meringue is ready, fan open a gallon-sized freezer bag and rest, one point down, in a deep cereal bowl (or small prep bowl) to hold it upright and support it while you add the meringue.
Spoon meringue into the open piping bag. Twist the bag closed, and cut the pointed tip off the end of your filled piping bag. (Start with a very small tip; you can always make it bigger if necessary in a minute.)
Begin piping equal amounts of caps and stems onto your cookie sheets. The stiffness of the meringue should allow you to pull the caps upward and remain upright. When rounding your caps with the piping bag, make sure you disconnect your bag somewhere other than the very tops of the little domes, or they will dry with pointed tops like witch hats, which you probably don’t want. If you do want to perform any minor smoothing before baking, wet your fingertips with water first to avoid sticking or unintentional pulling of the meringue.
Once all the meringue has been piped, they’re ready to bake. If you like, you can sprinkle the tops of the wet mushroom caps with cocoa powder to resemble dirt. You could also, alternately, make your mushrooms darker in color by whipping a small amount of cocoa powder into the meringue when you add the cream of tartar. It’s up to you.
Place the cookie sheets into the oven, shut the door, and IMMEDIATELY turn the oven completely off. Leave the mushrooms in the turned-off oven for at least 2 hours, or longer if you have another task to accomplish before finishing up the mushrooms. Don’t open oven door until you’re ready to take them out. Checking on them is not necessary; they won’t burn because the oven is no longer running. Once baked, carefully loosen the caps and stems from the cookie sheet individually, taking your time. When all are loose, take a small, sharp knife and gently chisel a small, round nook in the center of the underside of each mushroom cap. This will create a space for the point of the stem to rest and keep them connected later.
Heat chocolate in the microwave for one minute on HIGH power; stir well and recover. Return to the microwave and continue heating for 15-20 second intervals, removing to stir each time. Don’t overheat or it will gum up on you!
When chocolate is melted, use a butterknife to smear chocolate around the underside of each mushroom cap, being sure to let a little sink into the stem hole you created. As soon as you coat each cap bottom, immediately insert the pointed top of a stem piece and press gently.
Place the assembled mushroom upside down (stems up) on the cookie sheet and allow to rest this way until chocolate has cooled and hardened, sealing the stem inside the cap.
Store in an airtight container in a dry place. (NEVER REFRIGERATE!!!)