Preheat the oven to 200F (95C).

Add the egg whites, cream of tartar and sweetener to a stand mixer bowl, then whisk until soft peaks form.

Spoon a third of the mixture into a separate bowl and set aside.

With the remaining two thirds, add the vanilla and whisk until stiff peaks form. Transfer to a separate bowl.

Return the one third mixture to the stand mixer. Combine the water and cocoa powder together in a small bowl to form a paste. Add it to the stand mixer and whisk until stiff peaks form.

Gently fold the vanilla mixture into the cocoa mixture with just a few strokes.

Spoon the combined mixture into a piping bag fitted with a large star nozzle. Pipe out onto a baking tray lined with silicone mat or baking parchment. This recipe makes about 24 meringues.

Bake for one hour, turn off the heat, and leave the meringues in the oven with the door closed for three hours or until crisp.

Store in an airtight container.