01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a large bowl, beat unsalted butter, creamy peanut butter, granulated sugar, and packed light brown sugar until light and fluffy using an electric mixer.
03 - Beat in egg and vanilla extract until fully incorporated.
04 - In a separate bowl, whisk together all-purpose flour, baking soda, and salt.
05 - Gradually add dry ingredients to the creamed mixture, mixing just until combined.
06 - Scoop tablespoon-sized balls of dough onto prepared baking sheets, spacing approximately 2 inches apart.
07 - Bake for 8 to 10 minutes, until edges are set and lightly golden.
08 - Remove baking sheets from oven and immediately press a mini peanut butter cup into the center of each cookie. Let cool on sheet for 5 minutes before transferring to a wire rack.
09 - After cookies have cooled, transfer melted chocolate chips to a piping bag or zip-top bag. Pipe 3 to 4 legs on each side of the peanut butter cup to form spider legs.
10 - Dab a small amount of melted chocolate on the back of each candy eye and affix two eyes to each peanut butter cup. Allow chocolate to set before serving.