The first time I experimented with this recipe, I used a very dark, bittersweet chocolate (as a rule, I tend to prefer dark chocolate to milk chocolate). I can emphatically say that it was not a success. When you want to re-create the toasty, comforting taste of your childhood s'mores (always my favorite part of camping!), only milk chocolate will do. If you don't have the time, patience, or equipment necessary to make the marshmallow fluff (but try it; it's worth it!), you can place whole marshmallows over the cooled pie filling and toast those instead. It won't be as beautiful as the recipe below, but on what planet could toasted marshmallows be bad?
For Graham Cracker Crust: Preheat the oven to 350 degrees F (175 degrees C).
Crumble the graham crackers into the work bowl of a food processor and process until finely ground. Alternatively, you can put them in a bag and whack them with a rolling pin until finely crushed. Pour the butter into the crumbs and mix (hands are best for this) until the butter is fully incorporated and the texture is that of wet sand. Firmly press the crumbs against the sides of a 9-inch (23-centimeter) pie pan, then against the bottom of the pan (the underside of a measuring cup works well for smoothing the bottom crust). Chill the crust for at least 15 minutes to help prevent it from crumbling when serving. Bake the crust for 10 minutes, or until lightly browned. Remove it and allow it to cool before filling.
For S'mores Pie: Preheat the oven to 350 degrees F (175 degrees C).
Make the filling: In a saucepan, heat the cream over medium-high heat until it is scalded. Pour it over the chocolate in a heatproof bowl and let it stand for 1 minute. Whisk it thoroughly until combined into a glossy ganache. Whisk in the egg and salt until fully incorporated.
Put the crust on a baking sheet. Pour the chocolate filling into the crust and bake it for 20 to 25 minutes, until the filling has just set and is still slightly wobbly in the center. Remove the pie to cool completely.
Make the topping: In the bowl of a stand mixer or in a large heatproof bowl, sprinkle the gelatin evenly over 2/3 cup (160 milliliters) water. In a clean, heavy saucepan, combine the sugar, corn syrup, and another 2/3 cup (160 milliliters) water. Cook the sugar mixture over medium-high heat, stirring only at the beginning to dissolve the sugar, and boil it until a candy thermometer reaches the hard-ball stage (260 degrees F/130 degrees C). When the sugar is close to reaching this stage, turn on the stand mixer with the softened gelatin (or quickly beat the gelatin in your bowl to blend).
Once you've reached the right temperature, turn on the stand or hand mixer to low speed, and slowly pour the hot syrup in a steady stream into the gelatin while mixing. Try to avoid the sides of the bowl and aim for the space between the beater and the side. When all of the syrup is in, increase the speed gradually to high to avoid splashing, and continue to beat until the mixture is very thick and has tripled in volume, about 5 to 10 minutes. Add the vanilla, beat for a minute more, and then pour the topping over the pie. It will slowly spread to cover the surface, or you can use a spatula to spread it.
Allow the topping to cool at room temperature or in the fridge until it has set, about 30 minutes. If you are using a torch (the preferred method), make sure the area you are working in is clear of any plastic, paper, or other flammable items, and that the surface you are working on is fireproof (steel, marble, etc.). You can put a baking sheet under the pie to protect your countertops. Light the torch and start to lightly toast the surface of the pie, going darker or lighter according to your preference (I like my marshmallow pretty scorched, but that's me!). When the pie is perfectly bruleed, turn off the torch, and allow the pie to cool for 10 minutes.
Your pie is now ready to serve, or you can keep it in the fridge for up to 1 week. To cover, spray foil or plastic wrap very lightly with oil spray to prevent it from sticking to the topping. For easier slicing, run your knife under hot water first to prevent the marshmallow from sticking to the blade.