Pre-heat your oven to 225ºF and line a baking sheet with parchment paper
Bring 2 inches of water to a simmer in a pot. Place a clean stainless steel mixing bowl over the water. It shouldn't touch the water.
Combine your egg whites and sugar and whisk to combine. Occasionally whisk as it's heating to distribute the heat and dissolve the sugar.
Once your egg whites are at 110ºF (or when you don't feel any grains of sugar between your fingers) you're read to whip
Place the bowl on your stand mixer with the whisk attachment. Whisk on med for one minute, add in cream of tartar, salt and flavoring.
Bump up to high and let whip until you reach STIFF peaks.
Now you are ready to pipe your meringue onto a parchment-lined baking sheet into your mushrooms! Note: make sure your parchment sits completely flat on your baking sheet by placing dollops of meringue under each corner and pressing it flat against the pan.
Place piping tip into a piping bag. Fill your bag with your meringue.
To make the caps of the mushrooms, hold your piping bag straight up and down and squeeze to form the mushroom cap and pull up. There will be a little peak and that is okay, we will take care of that in a minute.
Once you have formed all your caps, use a tiny bit of water on your finger tip and gently smooth the top of the meringues.
For the stems, you hold your piping bag straight up and down again, touch the tip to the parchment, squeeze a bit to attach the meringue to the parchment then slowly move your hand up while squeezing. The base should be a bit thicker than the top. Make your stems about 2" tall.
Bake for about 2 hours, then turn off the oven but do not take them out. Let them sit in the oven until they are completely cold. I leave mine in overnight.
Meringue mushrooms can be stored in a ziplock bag unrefrigerated for up to two weeks.