Preheat the oven to 350 degrees. Line two baking sheets with parchment paper or a silicone baking mat (my fave) and set aside.
Combine the butter, peanut butter, 1/2 cup sugar and brown sugar in a large bowl, or the bowl of an electric mixer. Beat with a hand mixer or the paddle attachment until combined and fluffy, about 2 minutes.
Stir in the egg and vanilla extract.
In a medium measuring cup or small bowl, whisk together the flour, baking powder, and baking soda.
Stir into the peanut butter mixture until just combined, about 2 minutes.
Scoop the dough into 1 inch circles. Roll in the remaining 1/4 cup sugar and place on the prepared baking tray, each cookie roughly 2 inches apart.
Bake for 12 minutes, or until the cookies are lightly browned around the edges.
Remove from the oven and immediately press two round chocolates into the cookie to form the spider body.
Let the cookies cool about 5 to 10 minutes.
Place the chocolate chips into a zip top bag. Heat for 30 seconds on the defrost setting to melt. If needed, mix by squeezing the bag and heat for an additional 15 to 20 seconds to melt any remaining pieces.
Snip a small piece from the corner of the bag with kitchen scissors. Carefully pipe the legs, starting close to the body of the spider and ending at the foot.