In a large mixing bowl fitted with a paddle attachment, cream butter and sugar for 4-5 minutes until light and fluffy. Add in the peanut butter and mix for another 1-2 minutes. Add in the eggs and vanilla, mix to combine.
To the wet ingredients, add in the flour, baking soda, and salt, mix until fully incorporated.
Cover and chill dough for 25-30 minutes. Using a 1 oz. portion scoop or measuring spoon, scoop out 1 oz. scoops of dough. Use you palms to roll into smooth balls, then roll in sugar.
Preheat oven to 350 degrees F. Line a sheet pan with parchment paper and arrange cookies 2-3 inches apart.
Bake in a 350 degree oven for 9-11 minutes until golden brown, the cookies will still be very soft. Let sit for a few minutes after baking, then transfer cookies to a wire rack to cool completely.
After cookies has cooled for a few minutes, press a Reese's peanut butter cup into the middle of each cookie*. Press two candy eyes onto each peanut butter cup*.
Add melted chocolate to a small piping bag or plastic sandwich bag. Snip off a very small corner, and pipe the legs onto each cookie*. Let cool completely and enjoy. Leftover cookies can be stored in a airtight container for 3-4 at room temperature.
Notes
*Let the cookies cool for about 5 minutes after baking before adding the Reese's cup or the cups melt down too much. Popping the Reese's in the freezer for a few minutes prior can also help stop the candies from melting to much. *The candy eyes should stick right onto the Reese's cup as it get's a little melty from the warm cookie. If they don't stick on their own, use a dot of melted chocolate to adhere them. *See images above for reference on how to decorate the cookies. Spider legs can also draw on by dipping a toothpick into melted chocolate or use black twizzlers or a small tube of gel icing.