In a stand mixer, combine lukewarm milk, lukewarm water, instant yeast, granulated sugar, all-purpose flour, melted unsalted butter, and salt. Mix on low speed until combined, then knead the dough for 6-8 minutes until smooth and elastic.

Let the dough rise in a warm place for about 15 minutes until it has visibly puffed up.

In a medium saucepan over low heat, combine cocoa powder, heavy whipping cream, chocolate chips, and granulated sugar. Stir continuously until smooth, then remove from heat and mix in crushed graham cracker crumbs.

Once the dough has risen, roll it out into a rectangle. Spread the chocolate filling evenly, roll tightly into a log shape, and slice into 8-10 pieces.

Preheat the oven to 350°F (175°C). Let the rolls rise for another 15 minutes and then bake for 25-28 minutes until golden brown.

In a double boiler, whisk egg whites and sugar until warm. Beat until stiff peaks form, add cream of tartar and vanilla, then beat until glossy.

Spread meringue over the rolls and broil for 2-3 minutes until lightly golden. Let cool slightly before serving.