Preheat the oven to a low 200°F (95°C) and line two baking sheets with parchment paper.

Carefully separate your egg whites from the yolks, ensuring your mixing bowl and whisk are impeccably clean and grease-free.

In a large bowl, beat the egg whites and a pinch of salt on medium speed until soft peaks form; if using, add cream of tartar now.

Gradually add the granulated sugar, a tablespoon at a time, while continuing to beat on medium-high speed until the meringue is glossy, thick, and holds stiff peaks, then stir in the vanilla extract.

Sift the cocoa powder over the meringue and gently fold it in with a rubber spatula until just combined.

Transfer the meringue into a piping bag with your desired tip, then pipe small rosettes or kisses onto the prepared baking sheets, leaving space between them.

Bake for 1 hour 30 minutes to 2 hours, or until the meringues are completely dry and crisp.

Turn off the oven but leave the meringues inside with the door slightly ajar for at least another hour, or even overnight, until completely cool.