In a large bowl, combine the egg whites, cream of tartar, and salt. Whip until soft peaks form.
Gradually add the sugar, whipping until the mixture is stiff and glossy.
Gently fold the sifted cocoa powder into the meringue until evenly incorporated.
Fit a piping bag with a 1/2" or larger round tip and spoon the meringue into the bag.
Position the tip and bag directly over the prepared pan, and pipe the meringues onto the parchment, leaving 1" of space between the meringues.
Place the meringues into the preheated oven, then turn the oven off.
Let the meringues sit in the oven (keep the door closed) overnight, or until the oven is completely cool.
Remove the meringues from the oven.
To temper the chocolate, place 1 1/2 cups (255g) of chocolate in a temperer or in a double boiler and melt until completely smooth.
Remove the melted chocolate from the heat and gradually stir in the remaining 1/2 cup (85g) chocolate.
Keep stirring until the chocolate is fully melted and warm to the touch; it should be between 86° and 88°F.
To ensure that the chocolate is in temper, you can dip the tip of a knife into the bowl, and let it sit for 3 to 5 minutes. The chocolate should harden and become shiny.
Dip half of each meringue into the chocolate, allowing the excess chocolate to drip, and return them to the parchment-lined baking sheet to set.