Preheat the oven to 375°F. Grease the inside of a 9" springform pan.
Crush the graham crackers until fine. Melt the butter and stir in the crumbs until moistened. Use the back of a measuring cup to firmly press the graham cracker crumbs into place.
Bake for 10 minutes. Allow 30 to minutes to cool completely.
Place a few inches of water in the bottom of a pot and bring it to a simmer. Pour the chopped bittersweet chocolate into an oven safe bowl. It should be large enough to fit on top of the pot without touching the water. Melt the chocolate, stirring occasionally.
While the chocolate melts, place the heavy cream, sugar, and vanilla extract in the bowl of a stand mixer. Use the whisk attachment to whip the heavy cream to stiff peaks.
Once the chocolate is done melting, remove it from over the water. In four additions, gently fold in the whipped cream. Pour the chocolate filling into the baked graham cracker crust. Chill in the refrigerator for 4 hours.
Toasted Marshmallow Topping
Pour ¼ cup of water into a small bowl and sprinkle the gelatin on top. Allow to sit.
Put the additional 2 tablespoons of water, sugar, and corn syrup into a small pot fitted with a candy thermometer. Bring it to boil over a medium heat.
While the syrup mixture heats, put the egg whites and cream of tartar into the bowl of a stand mixer. Use the whisk attachment and put the mixer on medium speed. Whip the eggs to soft peaks.
Once the syrup mixture reaches 240°F on the candy thermometer, turn off the heat and gently stir in the gelatin mixture. Once the gelatin is dissolved, turn the mixer on medium and slowly pour the syrup mixture into the mixer in a thin stream.
Once the syrup is completely incorporated, turn the speed to high and whip for 10 minutes. Add in the vanilla extract and whip for a few minutes more. The topping should be thick, glossy and room temperature.
Remove the filled graham cracker crust from the fridge and spoon the marshmallow topping over the top. Use the back of the spoon to sculpt the topping into the desired shape. Allow to set for 10 minutes then use a kitchen torch to toast the marshmallow topping.