Make the graham cracker crust:

1. Preheat oven to 350°F.
2. In a medium mixing bowl, combine graham cracker crumbs, sugar, and melted butter until evenly moistened.
3. Transfer the mixture into a 9-inch pie dish. Press firmly into the bottom and up the sides of the pan using the bottom of a measuring cup.
4. Bake for 8-10 minutes, until lightly golden and fragrant.
5. Remove from the oven and allow to cool completely.

Make the chocolate ganache filling:

1. Place the chopped chocolate into a medium heatproof bowl.
2. In a small saucepan over medium heat, heat the heavy cream until steaming and small bubbles begin to form around the edges. Do not allow it to boil.
3. Pour the hot cream over the chocolate and let sit undisturbed for 2 minutes.
4. Whisk until smooth and glossy.
5. Add the butter, vanilla extract, and salt. Continue whisking until fully incorporated and silky smooth.
6. Pour the ganache into the cooled graham cracker crust and spread into an even layer.
7. Transfer to the refrigerator and chill for 2 to 3 hours, or until fully set.

Make the marshmallow topping:

1. Fill a small saucepan with 1 inch of water and bring to a gentle simmer.
2. In the bowl of a stand mixer or a large heatproof bowl, combine egg whites, sugar, cream of tartar (if using), and salt.
3. Place the bowl over the simmering water, making sure the bottom of the bowl does not touch the water.
4. Whisk constantly until the sugar has dissolved and the mixture reaches 160°F on an instant-read thermometer, about 4 to 5 minutes.
5. Transfer the bowl to a stand mixer fitted with the whisk attachment and beat on high speed for 6 to 8 minutes, until thick, glossy, and stiff peaks form.
6. Add vanilla extract and beat for another 30 seconds.

Assemble the pie:

1. Remove the chilled pie from the refrigerator.
2. Pile the marshmallow topping onto the pie and spread it all the way to the edges, creating decorative swirls and peaks with the back of a spoon or an offset spatula.
3. Use a kitchen torch to toast the marshmallow topping until golden brown.
4. Alternatively, place the pie under the broiler for 30 to 60 seconds, watching it constantly, as the marshmallow topping can go from golden to burnt very quickly.

Serve:

1. Allow the topping to set for 10 minutes before slicing.
2. Garnish with crushed graham crackers, mini marshmallows, or chocolate shavings if desired.
3. Serve chilled or at cool room temperature.