Preheat the oven to 350°F and lightly grease four cups of a muffin tin. Divide the cookie dough into four equal pieces, press each into the bottom and slightly up the sides of a muffin cup, and bake for 10 to 12 minutes until golden. Let the cookie cups cool in the tin for a few minutes before removing them to a wire rack.

While the cups cool, place the egg whites and cream of tartar in a clean mixing bowl. Beat on medium speed until soft peaks form.

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

Spoon the meringue into a piping bag fitted with a round tip or a zip-top bag with one corner snipped off. Pipe ghost shapes onto each cooled cookie cup.

Press two mini chocolate chips into each meringue ghost to form eyes. Return the cups to the turned-off oven with the door slightly open for 10 minutes to set the meringue.