Place the white chocolate chips in a microwave-safe bowl and heat in 30-second intervals, stirring between each, until fully melted and smooth.

Dip each large marshmallow into the melted white chocolate, coating it on all sides, then set it on a parchment-lined tray to harden slightly.

Melt the dark chocolate chips in the same way and transfer to a small piping bag or zip-top bag with a tiny corner cut off.

Pipe simple ghost faces onto the coated marshmallows and let them set for a few minutes.

Spread the crushed chocolate sandwich cookies across the center of a serving board to form the graveyard dirt base.

Stand the rectangular chocolate cookies upright in the crushed cookies to act as tombstones.

Arrange the ghost marshmallows around the tombstones on the board.