Preheat your oven to 350ºF. Using a 9" pie plate, lightly butter to prevent sticking. If you use a non-stick or glass pie plate you can omit this step.

Pulse the graham crackers in a food processor until finely ground. Alternatively, you can use a clear plastic bag and a rolling pin to crush them.

Next melt the butter and add to the graham crackers, along with the sugar and salt. Mix together until evenly combined. Press the mixture into the pie plate, making sure to evenly cover the bottom and sides.

Bake for about 12 minutes, or until it just starts to firm up. Not too long as it will be baked again with the chocolate filling.

Once done, place onto a cooling rack and let cool at room temperature for approx. 30 to 45 minutes.

Keep oven at 350°F for the filling.

Roughly chop the chocolate and place into a large bowl. In a medium-sized pot, bring the cream just to a boil. Once boiling, turn off the heat and pour the hot cream over the chocolate. Let sit for about a minute. Gently whisk until the chocolate is melted and the mixture is smooth. See the note in Step 3 for adding the salt (salt can be added at this point or after the pie bakes).

Next, gently whisk in the egg until evenly combined. Pour into the crust.

To bake the pie (350°F), cover the edge with a pie shield or cover the edges with a piece of foil.

Bake the pie for about 25 minutes or until the filling is just set. It should still shake or jiggle slightly in center. Once done, place onto a cooling rack and let cool to room temperature, about 1 hour.

If desired, lightly sprinkle the chocolate with a bit of fleur de sel as soon as it comes out of the oven. This will give the pie a nice sweet/savory contrast.

Note: Alternatively, you can add a pinch or two of salt to the chocolate and cream before you bake it.

Note: You will need a candy thermometer to make the marshmallow topping.

In a large, deep heat-proof bowl, sprinkle the gelatin over a 1/4 cup of the cold water. Let stand until softened, about 1 minute.

Next, in a clean heavy pot, stir together the sugar, corn syrup, a pinch of salt, and the remaining 1/4 cup of water. Bring to a boil over medium heat, stirring until the sugar is dissolved. Boil this mixture until the thermometer registers 260°F (or 126°C), about 6 minutes or so.

Using an electric mixer, quickly beat together the water and gelatin. With the mixer set to medium speed, carefully start to pour in hot syrup in a slow and steady stream. Try to avoid hitting the beaters and side of bowl with the syrup.

Once all of the syrup has been added, increase the speed to high and continue beating until the mixture has tripled in volume, is very thick, and holds a peak. This should take about 7 to 10 minutes.

Next, add the vanilla and beat just until combined.

Now immediately spoon the topping over the cooled pie filling. Gently spread the mixture to evenly cover the top of the pie.

Chill, uncovered for about 1 hour. Cover loosely with a piece of lightly oiled plastic wrap (oiled side down) and chill for at least 3 more hours.

Just before serving the pie, transfer it to a baking sheet.

There are two ways to obtain a nice brown crust on top.

1) Preheat the broiler. Cover the edges of the pie with a pie shield or foil. Broil 3 to 4 inches away from the broiler, rotating the pie if necessary. Keep an eye on it and let it cook just until golden. This should take approximately 2 to 4 minutes.

2) Use a blow torch. Carefully turn on the torch and use the flame to color the marshmallow topping.

Once done, let the pie cool slightly. To serve the pie, dip a sharp knife into a tall jug of very hot water. This will make it easier to slice. Clean the knife and dry on a towel each time you cut a slice.

This pie is very rich so a small piece is plenty.