Preheat oven to 130⁰C (265⁰F) and place the oven rack in the low/center of the oven. Line a baking sheet with parchment paper.
Put the egg whites and sugar in a stainless steel bowl and whisk to combine. Place the bowl over a saucepan of simmering water and, stirring constantly, heat the mixture until the sugar has melted (about 3-5 minutes) – dip a teaspoon into the mixture and taste – if there are no more gritty sugar granules, it’s done. Remove from heat and wipe the bottom of the bowl to remove any condensation.
Transfer the egg white mixture to the bowl of your electric mixer, fitted with the whisk attachment and beat on high speed (start on low and gradually increase to high) until the meringue is stiff with glossy peaks (about 5 minutes). When it’s done the bowl should be cool to the touch.
Add the vanilla extract, if using, and beat to combine. Sift the cocoa powder over the meringue and with a large spatula, gently fold the cocoa powder into the meringue – if you want interesting swirls of color, don’t fully combine.
Before placing the meringues on the baking sheet, place a little of the meringue on the underside of each corner of the parchment paper – this will prevent the paper from sliding. With two spoons (can also pipe), place 6 mounds of the meringue on your prepared baking sheet. If you like you can sift a little more cocoa powder over the meringues and, with a fork, makes swirls and peaks (this part is enormous fun!!).
As soon as you put the meringues into the oven, reduce the oven temperature to 100⁰C (210⁰F) and bake the meringues for approximately 1¼ to 1½ hours, or until the meringues have a crisp outside crust and release easily from the parchment paper. If you break one open, the inside will be soft and gooey. The longer you bake the meringues, the firmer they will be inside.
Remove from oven and place on a wire rack to cool. The meringues can be covered and stored at room temperature for 2-3 days (depending on humidity).