Make the graham cracker crust:

1. Preheat the oven to 375?.
2. Place the graham crumbs, brown sugar, cinnamon, and salt in a food processor and pulse. Drizzle in the melted butter and pulse a few times until well-combined.
3. Spoon the crumbs into a 9-inch tart pan, preferably with a removable bottom. Press firmly into an even layer along the bottom and sides of the pan.
4. Place on a rimmed sheet plan. Bake for 5-7 minutes, until the crust is golden and set. Remove from the oven and let cool completely on a baking rack.

Make the dark chocolate ganache filling:

1. Add the cream to a large, heavy-bottomed sauce pot over medium heat. Bring just to a simmer, then remove from the heat and stir in the chopped chocolate. Stir until the chocolate is completely melted, and the ganache is smooth and shiny. Stir in the vanilla.
2. Pour the ganache into the cooled graham cracker crust and smooth out the top with an offset spatula. Gently tap the bottom once or twice against the counter to release any air bubbles. Sprinkle with sea salt.
3. Let cool on a baking rack until set, about 2 hours, or about an hour in the refrigerator. Keep refrigerated until ready to serve.

Make the marshmallow meringue:

1. Pour 1-1/2 inches of water in to a 3-quart pot, and bring to a simmer over medium-low heat.
2. Combine the egg whites, sugar, salt, and cream of tartar in the bowl of a stand mixer and place over the water. Working constantly, stir and scrape down the sides of the bowl with a rubber spatula until the mixture is thin and foamy, and reaches 175?. This should take about 10 minutes.
3. Remove from heat and transfer the bowl to a standing mixer fitted with the whisk attachment. Starting on low speed and working up to high speed, beat until the meringue is light and glossy with stiff peaks, about 5 minutes. Beat in the vanilla. Immediately add to the s’mores tart.

Assemble the s’mores tart:

1. Spoon the marshmallow meringue over the chilled ganache, adding swirls with a flexible or offset spatula. Place on sheet pan and carefully use a kitchen torch to toast the marshmallow meringue.
2. Alternatively, place on a pan on the middle rack of the oven and broil for 1-2 minutes, until the meringue is golden and toasted. Watch it like a hawk to be sure it doesn’t burn too quickly!