In a mixing bowl, sift together the flour, baking powder, and salt. Set aside.
In a separate bowl, cream the softened butter and granulated sugar together until fluffy.
Beat in the egg and vanilla extract until well combined.
Gradually add the dry ingredients to the wet mixture, mixing until the dough forms.
Divide the dough into two portions, flatten into discs, and wrap in plastic wrap. Chill in the refrigerator for at least 1 hour.
Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper.
Roll out the chilled dough on a floured surface to about 1/4-inch thickness.
Use Halloween-themed cookie cutters to cut out shapes, placing them on the prepared baking sheets.
Bake for 8-10 minutes or until the edges are lightly golden.
Allow the cookies to cool on the baking sheets for a few minutes before transferring them to a wire rack to cool completely.
Once your cookies are completely cooled, prepare your royal icing with your desired colors and decorate to your heart's content using piping bags, tips, and edible decorations.