Preheat oven to 350° F. Grease two cookie sheets or line them with parchment paper.
Combine softened butter and sugars, beat with an electric mixer until light and fluffy, about 1-2 minutes.
Add eggs one at a time and continue to beat for about 1 more minute.
Add vanilla and mix.
In a separate bowl, combine flour, baking soda, salt, and cocoa. Whisk together until there are no lumps, then slowly add the dry mixture to the butter mixture, combine well.
Stir in one cup of chocolate chips.
Form dough into golf-sized balls and place evenly spaced on cookie sheet.
Bake for about 9 minutes or until edges are set. The dough will look dome-shaped.
Remove cookies from the oven and set the oven to the “broil” setting.
Immediately press 3-4 graham cracker pieces into each cookie- This will slightly deflate it.
Carefully set about 5 mini marshmallows on top of the cookie. It’s tricky to get them to stay but just do your best.
Put cookies back into the oven on the center rack, while the oven is now set to “broil”. Cook for about 30 seconds or until marshmallows puff up and get toasty. Remove from the oven. If some of the marshmallows have fallen off the cookie, scoop up with a butter knife and set it onto the cookie. Let cool.
Chop the Hershey’s bar, and melt in microwave (cook 15 seconds at a time, then stir, repeat until it softens) being careful not to burn it. Then transfer the melted chocolate to a ziplock bag. Snip the corner, and drizzle chocolate on each cookie. Let cool, then serve.