Preheat your oven to 375°F (190°C) and line baking sheets with parchment paper. In a medium bowl, whisk together flour, baking powder, and salt. In a large bowl, cream together butter and sugar until light and fluffy, then beat in the egg and vanilla extract.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Divide the dough in half, flatten each half into a disk, and wrap in plastic wrap, then chill for at least 30 minutes. On a lightly floured surface, roll out one disk of dough to about 1/4-inch thickness and cut out shapes using Halloween-themed cookie cutters, then place them on the prepared baking sheets.

Bake for 8-10 minutes, or until the edges are lightly golden. Let cookies cool on the baking sheets for a few minutes before transferring them to a wire rack to cool completely. Once cooled, prepare the icing by whisking powdered sugar and milk until smooth, then divide the icing into separate bowls and tint with food coloring. Decorate your Halloween sugar cookies as desired, adding sprinkles if using.