• Grab an 8” or 9” square baking pan and line it with parchment paper, leaving some overhang. Set it aside.

Make the Chocolate Ganache

• Chop milk or semisweet chocolate bars finely and pop them in a bowl. Heat 1 ½ cups of heavy cream in a saucepan until it starts to bubble gently. Pour the heated cream into the bowl of chopped chocolate. Let it soften for around 2 to 3 minutes.
• Gently whisk the mixture until the chocolate melts and mingles with the cream. Cover the bowl with plastic wrap, and put it in the fridge.

Make the Marshmallow Meringue

• Toss granulated sugar, cream of tartar, and egg whites in a heat-proof bowl. Fill a saucepan with about 2 inches of water and place the prepared bowl over it so its bottom doesn’t touch the water.
• Whisk the mixture continuously for about 4-5 minutes while cooking until the granulated sugar is completely dissolved and the mixture becomes thinner. Turn off the heat.
• Fold in 1 teaspoon of vanilla extract at high speed using a stand or handheld mixer with a whisk attachment until stiff peaks form, about 5 to 6 minutes. The creme should hold its shape well when you hold the whisk upwards. Scoop out 1 cup of the creme in a bowl, cover it, and stash it in the fridge for about 2 days.

Assemble the Cake

• Start off with a very thin marshmallow meringue layer on the prepared pan’s bottom. Spread gently and be careful with the sticky meringue.
• Place a graham cracker layer over the meringue, which takes more than 4 sheets. Break each sheet into smaller pieces to fit snugly in the pan.
• Spread a marshmallow cream layer on top, followed by a cracker layer and a chocolate ganache blanket. Repeat until you finish with all 6 cracker layers, 4 marshmallow meringue layers (the thin bottom counted), and 3 chocolate ganache layers.
• Cover the pan tightly using plastic wrap and give it a chilling session in the refrigerator for 12 hours to 2 days.
• Take remaining meringue out of the refrigerator. If it looks stiff and flat, simply whip it up using a whisk for one minute or two.
• Take the cake out of the fridge and free it from the pan.
• Carefully peel off the paper and transfer the cake to a cutting board or a heat-proof serving plate. Top it with the remaining marshmallow meringue. Use a spoon to create swirls and peaks (optional). Torch the marshmallow topping using a kitchen torch for more depth of flavor (optional).