In a large mixing bowl, combine the graham style crackers, melted butter, and brown sugar, mixing until fully combined. Press the mixture firmly into the bottom of the prepared pan. Refrigerate while making the filling.
Using an electric mixer, beat 1½ cups heavy cream until soft peaks form. Transfer the whipped cream to another bowl. Add the cream cheese to the mixing bowl and beat until smooth, about 1 minute. Add the powdered sugar, 2 teaspoons vanilla, and salt, and beat until fully combined. Fold in the cooled melted chocolate and whipped cream until fully combined. Spread the mixture evenly on top of the crust. Refrigerate while making the topping.
Preheat the broiler and place the top oven rack about 6 inches rom the heat source. Line a baking sheet with parchment paper or a silicon baking mat. Spread the marshmallows in an even layer and place under the broiler until browned. About 3 minutes but watch closely so they don’t burn. Let cool.
In the bowl of an electric mixer, combine the marshmallow fluff, ½ cup of heavy cream, and 1 teaspoon vanilla. Beat on medium speed until thickened. Spread the topping on the filling.
Sprinkle the cooled marshmallows, chopped chocolate and graham crackers on top. Refrigerate for at least 4 hours before serving.