Whisk flour, baking powder, and salt. Separately beat butter and sugar until creamy, then mix in the egg and extracts.
Gradually incorporate the dry ingredients. Chill the dough for 30–45 minutes so the ghost shapes remain defined during baking.
Roll the dough about ¼ inch thick and cut rounded ghost silhouettes with gently scalloped or flowing bottoms.
Bake at 350°F (175°C) for 9–11 minutes, keeping the centers pale and allowing only the edges to turn lightly golden. Cool completely.
Spread or pipe a generous layer of ivory frosting over every cookie, creating subtle vertical lines to suggest flowing ghost fabric.
Add black icing eyes and mouths. Decorate individual ghosts with tiny buttercream flower crowns, colorful blossoms, miniature bouquets, or flower-shaped glasses.
Allow the decorations to set before arranging the cookies on a cooling rack or Halloween dessert platter.