Preheat the oven to 350 degrees and line a baking sheet with parchment paper.

In a mixing bowl, beat the softened butter and granulated sugar until light and fluffy.

Add the egg and vanilla extract, then mix until combined.

In a separate bowl, whisk the flour, baking powder, and salt. Gradually add this dry mixture to the wet ingredients and stir until a dough forms.

Roll the dough to 1/4 inch thickness on a lightly floured surface. Cut out ghost shapes with a cookie cutter and place them on the prepared baking sheet.

Bake for 8 to 10 minutes until the edges turn lightly golden. Cool the cookies completely on a wire rack.

In a clean bowl, combine the powdered sugar, meringue powder, and water. Beat until the icing reaches a smooth, pipeable consistency.

Transfer most of the white icing to a piping bag and outline and fill each ghost cookie. Let the base icing set for 10 minutes.

Mix a small amount of the remaining icing with black gel food coloring. Use a fine tip to pipe eyes and a mouth on each ghost.