In a small saucepan over low heat, heat 1 cup of the heavy cream until scalding (not boiling!). Remove from heat and pour in chocolate chips.
Allow mixture to sit for 5 minutes, then stir with a whisk to combine. By this point, chocolate should be fully melted. Spoon into a piping bag and place in the fridge until ready to layer.
In a standing mixer fitted with a whisk attachment, beat the remaining 2 cups of heavy cream until soft peaks form. Spoon in marshmallow fluff, and whip to combine further until stiff peaks form. Set aside.
Line the inside of a standard-sized loaf pan with plastic wrap on all sides. Working in layers and starting with the whipped cream mixture, spoon and spread the whipped cream, pipe and spread the ganache, and layer the graham crackers. It’s completely up to you how much you spoon on each layer– if you want more whipped cream, do it! More chocolate, do it!
Finish with a layer of the whipped cream, then place in the freezer while you make your meringue.
Place egg whites into a standing mixer fitted with a whisk attachment. Whip egg whites until soft peaks form.
Meanwhile, heat sugar and water in a small saucepan over medium heat until the mixture reaches 240°F. If you don’t have a cooking thermometer, use the ice water test– place a small amount of the boiling sugar in ice water. Once the sugar forms a soft, malleable ball, it’s ready.
Working slowly with the egg whites still in the mixer, turn your mixer speed to medium and slowly drizzle in the sugar. Continue to mix until the meringue forms stiff peaks.
Remove ice box cake from freezer and frost with meringue. Use a culinary torch to finish off and golden-i-fy the meringue, if you have it!