Preheat oven to 350°F (175°C). Line baking sheets with parchment.
Whisk flour, baking powder, and salt. In another bowl, beat butter and sugar until fluffy. Mix in egg, vanilla, and almond extract.
Gradually add dry mixture to form dough. Roll out to ¼-inch thickness. Cut into Halloween shapes.
Bake 8–10 minutes until edges are lightly golden. Cool completely.
Whisk powdered sugar with egg whites (or meringue powder + water). Add vanilla.
Divide icing into bowls, tint with colors, and transfer to piping bags.
Decorate cookies with spooky designs. Allow icing to set before serving.