Cream the softened butter and granulated sugar in a mixing bowl until light and fluffy. Add the egg, peanut butter, and vanilla extract; mix until well combined.
In another bowl, whisk together the flour, cornstarch, baking soda, baking powder, and salt. Gradually add to the wet mixture until just combined. Chill the dough for at least one hour.
Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper. Roll out chilled dough to about ¼-inch thick and cut into rounds using a cookie cutter.
Bake for 8-10 minutes until edges are set but centers remain soft. Cool on sheets for 5 minutes before transferring to wire racks.
To assemble, place an unwrapped chocolate kiss in the center of each cookie. Decorate with purple gel food coloring around the base of each kiss and sprinkle with Halloween decorations.