01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a large bowl, beat together unsalted butter, peanut butter, granulated sugar, and packed brown sugar until light and fluffy.
03 - Add egg and vanilla extract, mixing until well blended.
04 - In a separate bowl, whisk all-purpose flour with baking soda and salt. Gradually add dry mixture into wet ingredients, blending just until combined.
05 - Scoop tablespoon-sized balls of dough onto prepared sheets, spacing about 2 inches apart.
06 - Bake for 8 to 10 minutes, until edges are set and lightly golden.
07 - While cookies are still warm, press a mini peanut butter cup into the center of each cookie. Let cookies cool on the sheet for 5 minutes, then transfer to a wire rack.
08 - Once cookies are cool, pipe melted semisweet chocolate around each peanut butter cup to create 3 to 4 spider legs per side using a piping bag or zip-top bag.
09 - Use a small dot of melted chocolate to affix two candy eyes on each cup. Allow chocolate to set before serving.