Preheat your oven to 350 degrees F (165 degrees C).
Place the frozen mini marshmallows in the freezer.
Spray a 9x13 baking dish with cooking spray.
In a medium bowl, combine the graham cracker crumbs, granulated sugar, and melted butter. Press into the prepared baking dish.
Sift together the all-purpose flour, baking soda, and salt.
In a large bowl, cream together the melted butter, brown sugar, and granulated sugar until light and fluffy.
Beat in the vanilla, egg, and egg yolk until light and creamy.
Mix in the sifted ingredients until just blended.
Fold in the semi-sweet chocolate chips and 1 cup of the frozen mini marshmallows.
Scoop the dough over the graham cracker crust, gently pressing into an even layer.
Sprinkle remaining 1/2 cup of mini marshmallows on top.
Bake for 18 to 25 minutes, or until golden brown.
Remove from oven and let sit for 5 minutes. Add broken pieces of Hershey chocolate bars on top.
Cool completely before cutting into squares.