Preheat the oven to 350 degrees F.

In a medium bowl, combine the graham cracker crumbs, sugar and melted butter until it has the consistency of wet sand. Press the mixture into 8 4-inch tart pans. Place them on a sheet pan and bake for 10 minutes. Let the shells cool.

For the filling, place the chocolate and sugar in a large bowl. Heat the heavy cream in a saucepan over medium heat, when it starts to bubble at the edges, pour the cream over the chocolate. Let it stand for 5 minutes before gently whisking until smooth. Pour into the tart shells. Chill in the refrigerator until firm, about 1 hour.

For the topping, combine the egg whites, sugar and cream of tartar in a heatproof bowl over a saucepan of simmering water over low heat. (Make sure the water is not touching the bottom of the bowl.) Heat the mixture until it is hot to the touch and the sugar has melted, about 3 to 4 minutes. Transfer the sugar-egg white mixture to the bowl of a stand mixer fitted with the whisk attachment. Add the vanilla extract. Beat for 6-8 minutes until it becomes a light, soft meringue. Spoon the meringue over the tarts and toast with a kitchen torch.

Serve immediately or store in an airtight container in the refrigerator up to 3 days. The tarts are delicate, so it is bester to serve them in their pans.