Preheat your oven to 200°F (93°C) and line a baking sheet with parchment paper.

Ensure your mixing bowl and beaters are grease-free. Separate the egg whites from the yolks.

Beat the egg whites on medium speed until frothy and bubbly, about 2-3 minutes.

Add the cream of tartar and increase the speed to high. Beat until soft peaks form, about 2 more minutes.

Gradually add the granulated sugar one tablespoon at a time while beating until stiff, glossy peaks form, about 5-7 minutes.

Sift in the cocoa powder and fold it gently into the meringue along with the vanilla extract.

Transfer the mixture to a piping bag and pipe 1-inch swirls onto the baking sheet.

Bake for about 1.5 to 2 hours without opening the oven door.

Turn off the oven and leave the cookies inside to cool completely.

Once cooled, store cookies in an airtight container at room temperature.