Preheat oven to 200 degrees F. In a large bowl with an electric mixer beat the egg whites until frothy. Add the cream of tartar and granulated sugar 1 tablespoon at a time. Beat until the egg whites are stiff and shiny and the sugar granules cannot be felt in the whites. Beat in the vanilla, reduce speed to low and add cocoa until combined. With a spatula put the egg white mixture into a pastry bag fitted with a large star tip. Pipe 2-inch meringue "kisses" on a parchment paper lined baking sheet, at least 2 inches apart. Bake in the middle of oven for 2 hours. Turn off oven and leave the meringues in it for at least 2 more hours or until meringues are completely dry.