To Prepare Graham Cracker Crust:

Preheat oven to 350 degrees F.  Combine graham cracker crumbs, brown sugar and melted butter in a bowl until evenly moistened.  Press into the bottom and sides of a 9-inch pie pan.  This will make a thick crust (about 1/2-inch thick).   Bake for 6 to 8 minutes or until lightly browned.  Let cool to room temperature before filling.

Fill a medium-sized saucepan about 1/2 full with water.  Bring to a gentle simmer.  You will use this twice as a double-boiler.

To Prepare Chocolate Filling:

In a medium-sized heatproof bowl, whisk egg yolks, granulated sugar, cornstarch and salt together until pale yellow in color and thickened.  Set aside.

In another saucepan, bring the milk to a gentle boil.  Whisk about 1/2 cup of the hot milk into the egg yolk mixture.  Slowly stir in the remaining milk to the egg yolk mixture.  Set the bowl over the prepared simmering water and saucepan.  Cook the egg yolk-milk mixture for 5 to 7 minutes, whisking constantly.  The mixture should be thick and glossy.

Remove the bowl from the water bath.  Whisk in the coffee, vanilla and melted chocolate.  Let sit for 2 to 3 minutes to thicken slightly.  Stir in unsalted butter until smooth.  Cover the surface of the chocolate filling directly with plastic wrap.  Let cool for 30 minutes or until it reaches room temperature.

Pour cooled chocolate filling into the graham cracker crust.  Cover the pie with plastic wrap and set into the refrigerator for at least 2 to 3 hours to chill.

To Prepare Marshmallow Topping:

In the bowl of a standing mixer or heat-proof bowl, whisk together the egg whites, cream of tartar, and granulated sugar.  Place the bowl over the medium saucepan with simmering water from earlier.  Whisk the egg white mixture constantly until the mixture is warm, about 3 to 5 minutes, and the sugar has dissolved completely. Rubbing a dab of the mixture between your fingers should feel silky and smooth.

Place the bowl onto a standing mixer fitted with the whisk attachment; or use a hand-held mixer.  Add the vanilla to the egg white mixture.  On medium to high speed, whip all until firm peaks form and the topping is glossy, about 5 to 7 minutes.

Place marshmallow topping over the cooled chocolate filling and graham cracker crust.  Be sure to spread it to the crust’s edges.  If desired, use a piping bag fitted with a decorative tip to place the marshmallow topping on.   To achieve the browned marshmallow effect, use a kitchen blowtorch to gently brown the topping.  Or use your oven broiler to golden the marshmallow topping.  Be sure to watch as the topping browns to avoid burnt topping (Unless you prefer a burned marshmallow flavor!).

Store covered in the refrigerator for up to 5 days.