4 large egg whites (120 grams total), room temperature
1 cup superfine sugar (you can make this by grinding 1 cup + 2 teaspoons white sugar in a food processor)
1 teaspoon vanilla OR 1/4 cup cocoa powder
1 teaspoon white vinegar
2 teaspoons cornstarch
Bare pinch of salt
Optional: 1 cup mini chocolate chips
Instructions
Preheat oven to 300F. Line a couple of baking sheets with parchment paper.
Start with a clean, dry bowl and whisk or mixer. Beat egg whites until they form firm peaks.
Still beating, slowly add the sugar, followed by the rest of the ingredients. Beat just until a lifted whisk shows stiff peaks. Gently fold in the chocolate chips.
Use a pastry bag or zipper bag with a tip cut off to form little rounds, a couple tablespoons each (hey will not spread in the oven).
Bake for 35-45 minutes, or until hard and very slightly browned. Cool on a rack for at least 30 minutes.
Seal leftovers in airtight containers for up to a week.