Preheat oven to 300, line cookie sheet with parchment paper. With an electric mixer, beat the egg whites in a large bowl until soft peaks form. Gradually add the sugar and beat until stiff and shiny, but not dry. Put the cocoa powder into a sieve and stir with a spoon until it is sifted onto the egg whites. Fold the cocoa into the whites until fully mixed. Fold in the chopped hazelnuts. Transfer the mixture to a large, heavy saucepan. Set over medium heat and stir with a wooden spoon until the mixture is shiny and pulls away from the bottom and sides of pan, about 6 minutes. Drop the batter by teaspoonfuls onto the cookie sheet, about 2 inches apart. Bake until firm, about 25 minutes.
