How to Make It
Preheat the oven to 375°. Line two baking sheets with parchment paper.
In the bowl of an electric mixer, combine the egg whites, cream of tartar and a pinch of salt. Beat the egg whites on high speed until foamy, then add the sugar a little at a time and continue to beat until all of the sugar is added and the egg whites hold stiff, glossy peaks.
Sift the confectioners’ sugar, almond flour and cocoa powder over the egg whites, then gently fold the dry ingredients into the meringue. Transfer the batter to a piping bag with a plain tip. Pipe teaspoon-size rounds of batter about 1 1/2 inches apart on the prepared baking sheets, making about 60 rounds of batter.
Reduce the oven temperature to 325° and bake the cookies until they are firm on the outside, 10 to 12 minutes. Let the cookies cool to room temperature, then peel them off the parchment paper. Make sandwiches with pairs of the cookies, using about 1 teaspoon of Nutella per cookie. Serve.