Mix egg whites on medium speed with mixer until frothy, about 3-4 minutes. Add cream of tartar after peaks formed. Slowly add sugar until stiff peaks form. Gently fold in m&ms with a spoon.
Preheat oven to 200. Lightly grease a baking sheet and sprinkle with sugar or use parchment paper. Using a spoon, heap a large tablespoonful of batter onto the cookie sheet leaving about 2 inches in between.
Place on top rack of oven and bake about 45 minutes
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