Preheat your oven to 225ºF. and coat a baking sheet with nonstick cooking spray. beat the egg whites with an electric mixer set at high until foamy. Add the cream of tartar and salt and continue beating. Gradually add the sugar. When you have added 1/4 cup of sugar, mix the remaining 1/4 cup with the cocoa. Gradually add the cocoa and sugar mixture to the meringue and beat  until stiff peaks form. Add the vanilla and beat at medium speed just until blended. Spoon the batter by rounded teaspoonfuls onto the baking sheet, making either 12 large meringues or 24 smaller ones. Bake for 50 to 60 minutes or until the meringues are firm. They will not brown. Cool on a wire rack.