Prepare the candy. Place the unwrapped miniature peanut butter cups in the freezer while you prepare the cookies. Preheat the oven to 350°F (175°C) and line a baking sheet.
Cream the butter and sugars. Beat the softened butter, brown sugar, and granulated sugar until light and well combined.
Add the wet ingredients. Mix in the creamy peanut butter, egg, and vanilla until smooth.
Finish the dough. Add the flour, baking soda, baking powder, and salt. Mix only until a soft dough forms.
Shape the cookies. Scoop tablespoon-sized portions and roll them into balls. Coat each ball lightly in granulated sugar and arrange them several inches apart on the prepared baking sheet.
Bake. Bake for 8–11 minutes, until the cookies look set and the edges are lightly golden.
Add the spider bodies. Immediately press one chilled miniature peanut butter cup into the center of each warm cookie.
Cool completely. Leave the cookies on the baking sheet for about 15–20 minutes before transferring them carefully to a cooling rack.
Decorate. Melt the chocolate chips with a little neutral oil if needed. Pipe four chocolate legs on each side of the candy center.
Add the eyes. Use small dots of melted chocolate to secure the candy eyes. Allow the chocolate to set before serving.