Preheat the oven to 325 F. Line an 8×8 inch baking pan with parchment paper, or spray with nonstick baking spray.
Arrange 5 of the graham crackers in the bottom of the pan, breaking the last cracker to fit.
Prepare the brownie batter, spread it over the graham crackers, and bake as instructed. Cool brownies completely.
Spread the marshmallow fluff over the cooled brownies, and set aside.
Pour the cream into a small saucepan, and warm the cream over medium heat, just until hot and beginning to simmer around the edges. Remove from the heat, and stir in the chopped chocolate until smooth and creamy. Let cool for 15 minutes.Spread the ganache over the marshmallow fluff. Let it set for a few minutes, then gently swirl the marshmallow fluff and ganache together.
Crumble up the last graham cracker and sprinkle it over the brownies. Chill the brownies in the refrigerator for about an hour, to firm up and set the ganache.
Cut the brownies into squares, topping each with a piece of Hershey's chocolate.