1. Place the nuts on a small baking sheet, and bake at 350° F for 10 minutes, or until lightly browned with a toasted fragrance. Cool to room temperature.
2. Place 3 tablespoons of the toasted nuts in a mini-food processor, and process until finely ground. Set aside. (If you do not have a mini-food processor, try fitting the bottom portion of your blender in a pint jar to form a mini-blender. Or grind the nuts with a mortar and pestle.)
3. Place the egg whites in the bowl of an electric mixer, and beat on high until foamy. Add the cream of tartar and salt, and continue beating until soft peaks form. Still beating, slowly add first the sugar, 1 tablespoon at a time, and then the vanilla extract. Gently fold in the ground nuts and, if desired, the coarsely chopped nuts.
4. Transfer 1/4 of the egg white mixture to a separate bowl, and gently fold in the cocoa powder. Return the cocoa mixture to the original bowl, and gently fold the 2 mixtures together just enough to produce a marbled effect.
5. Line a large baking sheet with aluminum foil. (Do not grease the sheet or coat it with cooking spray.) Drop heaping teaspoonfuls of the meringue onto the baking sheet, placing them about 1 1/2 inches apart.
6. Bake at 250°F for 45 minutes, or until the meringues feel firm to a light touch. Turn the oven off, and let the meringues cool in the oven for 2 hours with the door closed. Remove the pan from the oven and peel the meringues from the foil.