Start with a batch of your favorite chocolate chip cookies. Let them cool completely before decorating. You can also use a package of store-bought cookies for a shortcut!
Insert a toothpick into each marshmallow and place them upright on a sheet pan lined with parchment paper or a silicone mat, then set aside.
In a small microwave safe bowl, combine the white chocolate chips and vegetable oil. Microwave in 30 second intervals, stirring in between until melted and smooth.
Dip each marshmallow into the melted chocolate, let any excess drip off, then return to the prepared baking sheet and transfer to the freezer for 10 minutes to set the chocolate coating.
Once the marshmallows are set, remove the toothpicks and rub your fingertip in a small circular motion over the holes to blend the chocolate seamlessly until the hole disappears.
Use the remaining melted chocolate to spoon a small circle (about 1/2 a tbsp) onto the center of each cookie. Using the back of the spoon, spread the mixture slightly to resemble a ghostly gown.
While the chocolate is still melted, place one marshmallow on top of the melted chocolate before it hardens.
Return to the freezer for another 10 minutes to set the chocolate.
Draw your ghost faces on the marshmallows and they’re ready to enjoy!