Start by making the marshmallow fluff. Add the sugar, corn syrup, water and brown sugar to a medium saucepan. Place the pan over medium heat. Stir the mixture to combine it then do not stir anymore. Bring the mixture to a boil then reduce the heat to a simmer. Let the sugar mixture boil into a clear syrup for about 6-7 minutes.
While the syrup is simmering, whip the egg whites. Add them to the bowl of a stand mixer fitted with a whisk attachment. Whip on medium speed for 1 minute or until a microfoam has formed. Add the cream of tartar and salt and continue whipping for 5-6 minutes or until soft peaks have formed. By this point, the syrup should have reached 240 F. With the mixer still going, slowly stream the syrup into the egg whites. Once all of the syrup is incorporated, increase the mixer speed to medium high. Whip to medium stiff peaks. Add in the vanilla bean paste and continue whisking for 1-2 minutes or until stiff peaks have formed.
To make the chocolate, place the heavy cream in a microwave safe bowl and heat for 1 minute. Once heated, pour the heavy cream over the chocolate chips and let set for 1 minute to allow the chocolate to melt. Mix the two together until smooth and creamy.
To assemble the cake, start by placing about 4 graham crackers in an even layer in the bottom of a greased 9x13 pan. Next, use a rubber spatula to spread roughly ⅕ of the marshmallow fluff onto the graham crackers. Top with a layer of graham crackers, about 7 ½. Spread another ⅕ of the marshmallow fluff onto the graham crackers then spread ½ of the chocolate mixture onto the marshmallow fluff. Top with about 10 ¼ graham crackers followed by ⅕ marshmallow fluff. Layer 7 ¼ graham crackers on top followed by ⅕ marshmallow fluff then the remaining chocolate mixture. Place 9 graham crackers on top then spread the remaining marshmallow fluff over the surface.
Once the cake is assembled, cover and place in the fridge to chill for at least 4 hours or up to overnight. Once you are ready to serve it, remove the covering. Use a kitchen torch to toast the marshmallow fluff on top until golden or to your preference. Slice and serve.
Storage:This icebox cake may be stored, covered, in the fridge for up to 2 days.Tips:
Don't skip the chilling time! Chilling the cake in the refrigerator is what transforms this dish from a crunchy graham cracker layered dessert to a soft icebox cake.
If you do not wish to make marshmallow fluff, you can use premade, store bought marshmallow fluff instead.
It is perfectly fine if you use more graham crackers than indicated in the recipe. The amount of graham crackers may change based on the shape of your pan. Feel free to change up the assembly of the layers to create an icebox cake all your own.