Roll the dough into a large 16-inch rectangle. Score the dough in half, then score 6 even squares on that half of the dough.
Top each section with two squares of chocolate, and top each square of chocolate with half of a marshmallow. Bring the other side of the dough over the chocolate and marshmallows.
Line an 8-inch baking pan with parchment paper. Using a bench scraper or sharp knife, cut the dough into squares, pinch the edges shut, and place onto the prepared baking pan. Cover and allow to rise for about 30 minutes, until puffy.
Glaze the dough with egg, then top with the graham cracker topping. Bake in a 350°F oven for 25-30 minutes. Allow to cool before eating, since the chocolate inside gets VERY hot. Pull apart and enjoy!