Line an 8X8 square metal pan with cling wrap. Make sure to stick it to the bottom of the pan and leave overhang to create a sling. This will help you lift the finished cake out of the pan.

Make the pastry cream

In a 2-quart stainless steel saucier, whisk together sugar, cornstarch, salt, egg yolks, and the milk

Place saucepan over medium heat and whisk constantly as the pastry cream begins to thicken. This should take about 8 minutes.

While it is thick, continue to whisk until mixture starts to bubble. once bubble let the mixture cook for just one minute longer then remove from the heat

Once off of the heat add in the chopped chocolate, the butter and the vanilla

Mix with a nonstick spatula until chocolate is completely melted and the mixture is homogenous. If you would like a really smooth pastry cream, now is when you can strain the mixture over a sieve. If you see clumps in your mixture, you MUST do this step. If it is smooth you can skip. Place mixture in a heat proof bowl and let chill in the fridge until its completely cool. This may take about an hour.

In a large bowl, add the heavy cream and the granulated sugar. Whip slowly with an electric mixer on low speed to prevent splattering, then gradually increase to medium speed. The cream will go from foamy to soft peaks that barely hold their shape, continue beating to medium peaks that hold but tip over slightly. Stop when the cream holds its shape but remains smooth and spreadable. this should take about 3-5 minutes with an electric mixer or 8-10 minutes by hand

Place a 2 quart saucepan with 2 inches of water in it over medium heat and bring to a simmer

In the bowl of a stand mixer, combine 1 ¼ cups granulated sugar and 4 large egg whites. Place this bowl over the saucepan of simmering water, making sure the bottom doesn't touch the water. Using a nonstick spatula, stir the mixture constantly for about 4-7 minutes until the sugar completely dissolves and the mixture reaches 160°F on a candy thermometer (to test this, scrape the nonstick spatula around the bowl and lift up, bringing some of the mixture with the spatula. Using your ring finger and your thumb, swipe a small amount of the mixture from the spatula and rub it in between your fingers. It will feel smooth rather than grainy)

Remove the bowl from the heat and attach it to your stand mixer fitted with a whisk attachment. Whip on medium speed, then increase to high speed, beating for 8-12 minutes until the mixture transforms into a thick, glossy marshmallow meringue. This will have stiff peaks that hold their shape! The bowl should feel cool to the touch when finished, and the meringue should be stable enough to spread and torch

Line the first layer of the pan (on top of the saran or cling wrap) with a layer of graham crackers. Feel free to break them into pieces to cover the bottom in one flat layer

Next, add ½ of the pastry cream on top of the graham crackers and smooth out with an offset spatula

Add ½ of the whipped cream and then another layer of graham crackers. Then add the other half of the pastry cream, another layer of graham crackers followed by the last bit of the whipped cream.

The layers will be as follows: Graham crackers, ½ pastry cream, ½ whipped cream, Graham crackers, Other half pastry cream, Graham crackers, Last bit whipped cream

Smooth out the top of the icebox cake and top with all of the marshmallow topping

Using a spoon, add some swoops and texture to the marshmallow and place entire pan into the freezer and let set in the freezer for at least 4 hours

Remove from freezer and cut into slices

Using a kitchen torch, torch the marshmallow meringue topping! If you do not have a kitchen torch DO NOT BROIL THIS, instead just leave the marshmallow un-torched and it will still be delicious!