For the Crust: Preheat the oven to 350 degrees F
Line an 8x8 inch pan with foil. Grease the foil lining with butter or cooking spray.
Combine all of the crust ingredients in a medium bowl.
Press the crust into the bottom of the pan in an even layer.
Bake for 10 minutes and then set aside.
For the Peanut Butter Layer: Sprinkle the peanut butter chips evenly over the still-warm crust.
Return the pan to the oven, which should be off. We will use the residual heat to melt the chips.
Allow the pan to sit in the oven for 5 to 7 minutes. When the peanut butter chips are nice and shiny, remove the pan from the oven.
Using an offset spatula, spread the melted chips over the graham cracker crust.
Set aside to set.
For the Chocolate Filling: In a heavy-bottomed sauce pan, place the chopped chocolate and the sweetened condensed milk.
Melt the chocolate in the milk over medium heat.
Once completely melted and combined, immediately pour into prepared crust.
Set aside while making the marshmallow topping.
For the Marshmallow Topping: Combine the sugar, corn syrup, water and salt in a small, heavy-bottomed sauce pan.
Place over medium heat. Boil until a candy thermometer reaches 240 degrees F.
While the sugar mixture comes to temperature, beat the two egg whites and cream of tartar in the bowl of a standing mixer fitted with a whisk attachment until soft peaks form.
When the sugar mixture comes to temperature, turn the mixer to low. Pouring down the side of the mixer bowl, in a slow steady stream pour the sugar mixture into the egg white mixture.
When all of the sugar mixture is poured into the egg mixture, turn the mixer to medium high. Beat for 7-8 minutes until the mixture is thick and glossy.
With about a minute left, add the vanilla.
Spread 2 cups of the marshmallow fluff over the chocolate filling.
Turn the oven to broil, and broil the top of the marshmallow until golden brown.
Cut into squares when ready to serve.