GRAHAM CRACKER CRUST

1. Preheat the oven to 350˚f / 180˚c. 
2. Place the graham crackers, sugar, and salt in the work bowl of a food processor. Pulse until the crackers are broken down into crumbs. Transfer to a medium sized bowl.
3. In a medium sized saucepan, heat the butter over medium heat. Once it has melted, continue to cook, stirring occasionally and watching very carefully, until it turns golden brown in colour, and begins to smell toasty. Pour into the graham cracker mixture, and stir well with a spatula. 
4. Press the crust mixture into a 9" removable bottom tart pan, pressing onto the sides, and then the bottom. Use a straight sided measuring cup or drinking glass to help you press the crust in tightly. Place the tart pan on a baking sheet.
5. Bake the crust for 10-12 minutes, or until beginning to brown around the edges. Remove from the oven and cool completely.

CHOCOLATE GANACHE FILLING

1. Place the chocolate and butter into a large heatproof bowl. Place the cream in a small saucepan, and warm over low heat until just shy of a simmer - you should see movement around the edges of the cream. Immediately pour the cream over the chocolate and butter, and cover the bowl with a lid or plate. Leave to sit for 5-6 minutes, then whisk vigorously to combine the chocolate and the cream. The mixture will look like it has split to begin with but keep whisking - it will come together and go glossy eventually!
2. Pour the chocolate filling into the cooled crust. Place in the fridge for 1 ½ to 2 hours, or until the filling has set completely.

MARSHMALLOW TOPPING

1. In the bowl of a stand mixer fitted with the whisk attachment, combine the cold water and gelatine. Mix well with a fork, and leave to bloom while you prepare the sugar syrup. 
2. In a medium pot, combine the water, corn syrup, sugar and vanilla. Heat over medium to high heat, stirring occasionally. Heat until the syrup reaches 240˚f / 120˚c, then remove from the heat and leave to cool to 210˚f / 100˚c.
3. Turn the mixer on to medium, and mix for a few seconds to help break up the bloomed gelatin. With the mixer running, VERY carefully pour the hot sugar syrup into the mixer. Turn the speed up to high, and whip for 5-7 minutes, until the marshmallow has doubled in volume, has turned white, and holds somewhat of a peak when you stop the mixer and lift out the whisk. 
4. Pile the marshmallow on top of the tart. Torch with a blow torch before serving.
5. Cut into slices with a knife that has been run under hot water and dried before each cut is made. Store leftovers in the fridge.