How to Make It
Microwave cream in a medium-size microwavable bowl on HIGH until boiling, about 45 seconds. Add chocolate chips to hot cream; whisk until smooth. Let stand at room temperature until ready to use.
Preheat oven to 350°F. Coat 3 (8-inch) round cake pans with baking spray; line with parchment paper. Stir together graham cracker crumbs, melted butter, and 1/3 cup of the sugar in a medium bowl. Divide crumb mixture evenly among prepared pans; press crumb mixture firmly into bottom of each pan.
Prepare cake batter according to package directions. Spoon batter evenly over graham cracker crusts in pans. Bake in preheated oven until a wooden pick inserted in centers of cakes comes out clean, 18 to 22 minutes. Let cool in pans on wire racks 10 minutes. Carefully invert cakes onto wire racks; let cool completely, about 1 hour.
Place 1 cake layer, graham cracker side down, on a serving plate or a cake stand. Spread top with half of the melted chocolate mixture, being careful not to let chocolate spill over cake sides. Top with second cake layer, graham cracker side down. Repeat spreading procedure using remaining melted chocolate mixture. Top with third cake layer, graham cracker side down. Chill until chocolate is set, about 30 minutes.
Meanwhile, pour water to a depth of 1 1/2 inches in a large saucepan; bring water to a boil over high. Reduce heat to low, maintaining a gentle simmer. Whisk together egg whites, salt, and remaining 1 1/3 cups sugar in bowl of a heavy-duty stand mixer. Crumple a large piece of aluminum foil, and shape into a ring about 2 inches high. Carefully place foil ring in simmering water in saucepan. Place mixer bowl on foil ring so that the ring prevents the bowl from touching the water.
Cook egg white mixture, whisking constantly, until mixture registers 160°F on an instant-read thermometer, 10 to 12 minutes (sugar should be dissolved). Transfer bowl to a stand mixer fitted with a whisk attachment. Beat mixture on low speed for 1 minute. Gradually increase speed to medium-high, beating until mixture is fluffy, glossy, and completely cool, 8 to 10 minutes.
Spread meringue frosting evenly over tops and sides of cake. Using the back of a spoon or an offset spatula, create peaks in frosting. Brown the frosting using a kitchen torch, creating a toasted marshmallow effect. Slice and serve.