Preheat the oven to 200 degrees F and line a baking sheet with parchment paper.

Place the egg whites in a clean mixing bowl and add the cream of tartar. Beat on medium speed until soft peaks form.

Gradually add the sugar while beating on high speed until stiff, glossy peaks develop. Mix in the vanilla extract.

Transfer the meringue to a piping bag fitted with a round tip. Pipe eight ghost shapes onto the prepared baking sheet, leaving space between each one.

Bake for 90 minutes, then turn off the oven and leave the meringues inside to cool completely without opening the door.

Combine the dark chocolate chips and heavy cream in a small bowl. Microwave in 20-second bursts, stirring between each, until smooth.

Spread or pipe a thin layer of the chocolate mixture onto the flat side of four cooled meringue ghosts. Top each with a second ghost to form a sandwich.