Preheat oven to 350F. Grease a 9×13 baking pan with cooking spray.
in a medium bowl, mix together the graham cracker crumbs and melted butter together until all is moistened. Press the mixture into the bottom of the prepared pan until it is evenly layered. Bake for 8-10 minutes just until the edges are lightly browned. TURN OFF THE OVEN.
Lay the Hershey’s chocolate bars on top of the graham cracker crust and put the pan back into the warm oven for 1 minute.
Pour the marshmallows on top of the chocolate, making sure that it’s evenly layered.
Put back in the oven and broil for 1-2 minutes until the marshmallows are golden brown. Do not step away from the oven. Keep a close eye the whole time and remove the pan from the oven as soon as it turns golden on top.
Let cool for 15 minutes on a wire rack, then place into the fridge for it to be completely set. Cut into squares.