In a large bowl, cream together softened butter (¾ cup, i.e., 1 ½ sticks), peanut butter (1 cup), light brown sugar (1 cup), and granulated sugar (1 cup) with an electric mixer on medium speed for 30 seconds. Add in vanilla extract (1 teaspoon) and eggs (2 large) and continue to mix for 10 seconds.
Add baking soda (1 ½ teaspoons) and mix on low speed for 10 seconds. Add all-purpose flour (2 ½ cups) and continue to mix until all flour is incorporated.
Scoop & roll dough into 1 tablespoon sized balls and place each in a greased, mini muffin tin.
Bake at 350℉ for 8 minutes. Remove from oven, and immediately press one mini Reeses peanut butter cup into the center of each cookie.
After a few minutes, the chocolate of the peanut butter cup will start to melt. Once this happens, gently press a green M&M into the top of each one with the "M" logo side facing down.
Place pan in refrigerator for 10-15 minutes to help the chocolate re-harden.
Once fully cooled, use a black edible food pen to draw a dot onto the top of each M&M for the pupil.
Allow to cool before removing from the cookies from the pan.
If not serving immediately, store in an airtight container for up to 5 days or freeze for long-term storing.