Preheat oven to 350°F. Line two baking sheets with parchment paper.
Beat butter with granulated and brown sugars until light and creamy, about 2 minutes. Add eggs and vanilla, beating until combined. Scrape down the bottom and sides of the bowl.
1 cup salted butter, 1 cup granulated sugar, 2/3 cup firmly packed light brown sugar, 2 eggs, 2 teaspoons vanilla extract
Add the flour, cocoa power, baking soda, and salt. Mix just until combined. At this point, you can bake the cookies right away or let the dough chill, covered with plastic wrap, for an hour or two for easier rolling.
2 cups all-purpose flour, 2/3 cup unsweetened cocoa powder, 1 teaspoon baking soda, 1/4 teaspoon salt
Scoop the dough and shape into 2 tablespoon-sized balls by rolling between the palms of your hands. Space them 2 inches apart on the prepared baking sheets. Bake for 9-11 minutes, just until done. Do not overbake as the cookies will finish setting up on the baking sheet as they cool
Immediately after removing the cookies from the oven, press an unwrapped peanut butter cup green side into the top of each cookie. Wait about five minutes for them to melt slightly from the residual heat of the cookies, then press googley eye candies into the soft chocolate. As the cookies finish cooling completely, the chocolate will set up again, albeit softer than before.
2 bags Reese's Franken-Cup Peanut Butter Cups, Googley eye candies