Preheat oven to 225F (105C) and line a large baking sheet with parchment paper. Set aside.

In a clean, dry large mixing bowl (use the bowl of a stand mixer if you have one), combine the egg whites, cream of tartar and salt and use the whisk attachment of your stand mixer or an electric mixer to stir on medium-low speed until foamy (about 30-60 seconds).

Increase mixer speed to high and gradually add sugar, about 1 Tablespoon at a time, stirring for about 20 seconds after each addition.

Continue to stir on high speed until meringue is thick, shiny, and has increased substantially in volume and you've reached stiff peaks. Sugar should also have dissolved (test this by rubbing a small bit of the mixture between your fingers, if it feels gritty, the sugar isn't dissolved).

Add vanilla extract and cocoa powder and, using a spatula, gently fold into the meringue until well incorporated and batter is uniform.

Fit a large disposable piping bag with a large tip (I used an Ateco 846 tip and piped into 1 ½" (4cm) swirls) and transfer meringue into prepared piping bag and pipe onto prepared cookie sheet. The meringue cookies won't spread and so can be piped close together, and you will want to bake all of the cookies at the same time, so make sure you leave enough space.

Transfer to center rack of 225F (105C) oven and bake for 1 hour, then turn off the oven but do not open the oven door. Leave the oven door closed and allow cookies to cool completely in the oven (1-2 hours) before removing.

Once cookies have cooled completely, place chocolate chips in a small microwave-safe bowl and melt in 20-second intervals (stirring well in between) until chocolate is completely melted.

Once chocolate has melted, dip meringues halfway into chocolate, remove, and return to a wax paper lined baking sheet for chocolate to harden before enjoying.