Make Cupcakes: Preheat oven to 350°F (175°C) and line a standard 12-cup muffin tin with paper liners. Prepare the chocolate cake batter according to the package instructions.

Bake Cupcakes: Divide the batter evenly among the cupcake liners. Bake the cupcakes according to the box instructions, or until a toothpick inserted into the center of a cupcake comes out clean.

Cool Cupcakes: Let the cupcakes cool completely.

Make Marshmallow Frosting: While the cupcakes are cooling (or even before baking), make the marshmallow frosting. In a small saucepan over medium heat, heat ½ cup of water until simmering. In a medium heatproof bowl, combine the egg whites and sugar, then carefully place the bowl on top of the saucepan to create a double boiler. Cook, stirring constantly, until the sugar is dissolved and the mixture is warm to the touch, about 5 minutes.

Whip Meringue: With oven mitts or a dry towel, carefully remove the egg white mixture from the saucepan; reserve the saucepan and water. Using an electric mixer on high speed (or attach the bowl to a stand mixer fitted with the whisk attachment), beat the mixture until it resembles marshmallow fluff and forms soft peaks, about 8 minutes.

Add Flavorings: Beat in the vanilla extract and salt. Transfer the frosting to a piping bag fitted with a large star tip.

Melt Chocolate: In a clean medium heatproof bowl, place the chocolate chips. Carefully place the bowl over the reserved saucepan of simmering water. Cook, stirring, until melted, about 4 minutes. Remove from heat and keep warm until ready to use.

Prepare Graham Crackers: Carefully break 2 graham crackers to form 12 (1″) squares; set aside. Transfer the remaining 3 graham crackers to a resealable plastic bag and smash with a wooden spoon or heavy pot to create fine crumbs. Transfer the crumbs to a shallow bowl or plate.

Assemble the Cupcakes Once cooled.

Dip in Chocolate: Dip the edges of each cupcake into the melted chocolate, rotating to coat the rim.

Coat in Crumbs: Dip the edge of each cupcake into the graham cracker crumbs and turn to coat.

Pipe Frosting: Pipe the marshmallow frosting onto the cupcakes.

Broil (Carefully!): Arrange the frosted cupcakes on a baking sheet and broil, watching closely, until the frosting is golden brown, about 30 seconds. This step requires extreme vigilance, as the frosting can burn very quickly.

Garnish: Garnish with the reserved graham cracker squares.