Start by preheating the oven to 350F, then line a baking sheet with parchment paper
Start by creaming the butter and sugar together using the paddle attachment of your stand mixer or hand mixer.
Add in the egg, and vanilla, and mix until everything is mixed together. Scrape the sides if needed.
Add the flour, baking soda, cream of tartar, salt, and cinnamon to the wet mixture and mix until just incorporated.
Using a small cookie dough scooper, scoop out 14 cookie dough balls, roll them in between the palm of your hands, then roll them in the cinnamon-sugar mixture. Place the cookies on the baking sheet making sure to leave 3 inches between each one.
Bake for 10 minutes. The cookies will be puffy and pretty soft still, don't worry about that, they will continue baking as they cool down. Let the cookies sit on the baking sheet for 5 minutes then top each cookie with an upside-down Reese's cup.
Once the peanut butter cup starts melting a little add the eyeball candies. Melt the milk chocolate, transfer it to a ziplock bag, snip a tiny piece of the tip, then pipe the spider legs on the cookies. Let the chocolate set before enjoying them.