Warm up the milk and water to a lukewarm temperature and pour them into your stand mixer bowl. Sprinkle in the instant yeast along with the granulated sugar and then add the all-purpose flour. Melt part of your butter and add it to the mixture along with the salt. Stir everything together until it combines well. Attach the dough hook and knead the dough for six to eight minutes, until it feels smooth and elastic. Cover the bowl and allow the dough to rest for 15 minutes so it can rise slightly. While the dough rests, prepare the filling by gently heating cocoa powder, heavy cream, chocolate chips, and sugar in a saucepan over low to medium heat. Stir in the melted butter, vanilla extract, and a pinch of salt, blending until the mixture is smooth. Remove from heat and once cooled, mix in the graham cracker crumbs. On a lightly floured surface, roll the dough out into a rectangle about 10 by 16 inches. Brush the surface evenly with melted butter, then spread the cooled chocolate mixture over the dough, leaving the edges clear. Sprinkle additional graham cracker crumbs on top. Roll the dough up tightly from one side, then slice into 8 to 10 pieces and place them in a greased baking dish. Heat your oven to 350°F (175°C) and bake the rolls for 25 to 28 minutes, or until they are golden brown. Let the rolls cool in the pan for ten minutes before adding the meringue topping. Make the meringue by warming egg whites and sugar gently in a double boiler, whisking as the sugar dissolves. Transfer the mixture to a stand mixer and beat until stiff peaks form while adding cream of tartar, salt, and half the vanilla extract. Spread the meringue generously on the cooled rolls, then carefully toast the topping using a kitchen torch or under a broiler until it turns golden brown.