• Preheat the oven to 350°.
• Line a baking sheet with parchment paper or a silicone baking mat. Set aside.

MAKE THE COOKIE DOUGH

• Place the butter, egg, vanilla extract, white sugar, and brown sugar into a large mixing bowl and beat with an electric mixer for 2-3 minutes.
• Add the flour and baking soda to the mixing bowl and mix until fully incorporated and a soft dough is formed.
• Add the chocolate chips to the mixing bowl and mix with a wooden spoon or rubber spatula until incorporated.
• Place the dough in the refrigerator and allow it to chill for one hour.

ASSEMBLE THE COOKIES

• Remove the chilled dough from the refrigerator, use a large cookie scoop out ¼ cup size balls of dough, and place them, evenly spaced, on a baking sheet. I was able to fit six cookies on a standard-size baking sheet.
• Use your hands to flatten the dough balls to form large, flat circles.
• Place one or two small Hershey bar squares in the center of each cookie.
• Place a marshmallow on top of the chocolate squares and press the sides of the cookies up around the marshmallows, leaving the tops of the marshmallows exposed.

BAKE AND DECORATE THE COOKIES

• Bake for 10 minutes, or until the bottoms of the cookies begin to turn golden brown and the marshmallows flatten out and become gooey. Be careful not to overcook or the marshmallows will melt and absorb into the cookies.
• Remove the cookies from the oven and allow them to rest on the baking sheet for 5-10 minutes before gently transferring them to a wire cooling rack to cool completely.
• Add a few sprinkles and candy eyeballs on top of the melted marshmallows.