Preheat the oven to 90℃/190℉.
Separate egg whites and yolks. Transfer egg whites to a large bowl.
Add cream of tartar and salt. Beat the egg whites with an electric mixer or stand mixer on low speed till frothy.
Add powdered sugar one tablespoon at a time while beating the egg whites at high speed. Sprinkle the sugar slowly.
After the last addition beat the egg whites on high speed (10-15 minutes) till stiff peaks appear. Add vanilla extract and mix till combined.
Place small dollops of meringue on the corners of the cookie sheet and press the baking paper down. Meringue will act as a glue to keep baking paper in place.
Use two spoons to scoop the meringue and place it on the cookie sheet with around a 1-inch distance between them. Pour 1 tsp of melted dark chocolate on top of meringues and use a toothpick to create swirls.
Bake in a preheated oven at 90℃/190℉ for 1 hour.
Switch off the oven and let the meringue cookies sit in the oven for 1 hour or overnight.