To make the dough, combine the flour, graham cracker crumbs, salt and sugar in a food processor. Pulse a few times to thoroughly combine. Add in the butter and pulse until it resembles coarse crumbs, the size of peas, about 8 to 10 times. Add the water, one tablespoon at a time, and process until the dough comes together. Divide in half and form each half into a disc and wrap each in plastic wrap. Chill for at least 1 hour or overnight.

To make the filling, place the chocolate and butter in a heatproof bowl. Set the bowl over a pot of simmering water, making sure the water doesn't touch the bottom of the bowl and stir until melted through, about 5 to 8 minutes. Remove from the pot and let cool. Once cool, whisk in the eggs, heat cream, sugar and vanilla until well combined. Cover with plastic wrap and chill until thick and set, about 1 hour.

Preheat oven to 350 degrees F. Line two baking sheets with parchment paper, and set aside.

Working with one half of dough at a time, place on a well-floured work surface and roll out to about 1/4-inch thick. Using a 5-inch round cutter, cut out into circles. Reroll and cut out as needed, placing on a baking sheet lined with parchment paper. Repeat with the second half of dough. Fill each circle of dough with about 1 tablespoon and a half of the chocolate filling. Fold the edges of the dough toward the center. Brush the edges with egg wash and sprinkle with turbinado sugar. Bake until golden brown around the edges and the filling has set, about 18 to 20 minutes. Remove from oven and let cool slightly.

Top each with 3 large marshmallows and either place under the broiler to toast or use a kitchen blowtorch to roast the marshmallows. Drizzle the top with melted chocolate and then sprinkle with crushed up graham crackers. Serve warm. Leftovers can be stored in the fridge for up to 3 days and rewarmed in the oven for a few minutes.