In a large bowl, cream together the softened unsalted butter with confectioners' sugar until light and fluffy, about 2-3 minutes using an electric mixer.

Beat in the egg and vanilla extract until fully incorporated.

In a separate bowl, whisk together the all-purpose flour, baking soda, cream of tartar, and salt.

Gradually add the dry mixture to the wet ingredients, mixing just until a cohesive dough forms. Be careful not to overmix.

Divide the dough into two discs, flatten slightly, and wrap in plastic wrap. Refrigerate for at least 30 minutes.

Preheat oven to 350°F (175°C) and line baking sheets with parchment paper.

On a lightly floured surface, roll the chilled dough to about ¼-inch thickness and cut out ghost shapes with a cookie cutter.

For extra-crisp edges, place the cut shapes on the baking sheet and refrigerate for another 10 minutes before baking.

Bake for 8-10 minutes, or until the edges are just lightly golden. The cookies should remain pale for that ghostly appearance.

Allow cookies to cool completely on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.

Prepare the icing by mixing powdered sugar with small amounts of milk until smooth. Add a tiny bit of corn syrup for shine if desired.

Pipe or spread the icing onto the cooled ghost cookies, then quickly add two mini chocolate chips for the eyes before the icing sets.

Allow the icing to set completely before serving or storing.