Add the butter and peanut butter to a large mixing bowl. Use an electric mixer to beat them together on medium speed until they’re mixed, about 30 seconds. Then, add in the brown and white sugar until mixed. Add the egg, milk, and vanilla extract and beat on a low speed until just combined.

Whisk together the flour, baking powder, baking soda and salt in a separate bowl. Then, add the dry ingredients to wet. Mix on a slow speed for about 30 seconds and increase to a medium speed. Mix until there are no dry streaks of flour.

Shape the cookie dough into a disc and wrap in plastic wrap. Place the cookie dough and the mini reese’s cups (still wrapped) in the refrigerator for one hour to chill.

After the cookie dough has chilled for one hour, preheat the oven to 350℉ and line two baking sheets with parchment paper.

Create 1.5-inch balls of dough and place them on the baking sheet about two inches apart. Bake each sheet of cookies one at a time one the middle rack for 10 minutes, just until the edges of the cookies firm up and the cookies begin to crack.. While the cookies bake, unwrap the reese’s cups and then keep in the refrigerator until it’s time to use them.

As soon as the cookies come out of the oven, gently press a reese’s cup into the center of a cookie. Then, move the cookies to a cooling rack.

Once the cookies are cool, pipe on the spider’s legs. Create eight legs by drawing four lines from the reese’s cup outward and down the cookie on each side. Dab two spots of icing to glue the eyes to the body of the reese’s cups.