Bake at 350 degrees for 8 minutes. Remove from oven, and immediately press one mini Reeses peanut butter cup into the center of each cookie.
After inserting the Reeses, allow the cookies to cool on a cooling rack (while still in the muffin pan) for about 20 minutes. At this point, your chocolate will likely still be melted so you should then place the entire pan in the fridge for about 15 minutes or until the chocolate sets. Once the chocolate is hardened, use a spoon to gently "scoop" out the cookies. This is where spraying the muffin tin before baking is crucial, otherwise your cookies will stick to the pan!