Combine the sugar and butter in the bowl of a stand mixer fitted with the paddle attachment. Beat for 1 to 2 minutes until creamy. Stir in the flour. If the mixture is too crumbly, you can add another tablespoon of butter.

Evenly divide the shortbread cookie crumbs into each cake pan. Using the back of a spoon, press the shortbread cookie crumbs into an even layer on the bottom of the pan.

In a stand mixer fitted with the paddle attachment, combine the flour, sugar, cocoa powder, baking powder, baking soda and salt. Mix for about 30 seconds.

In a separate bowl, combine all of the wet ingredients and whisk for a few seconds.

With the mixer on low speed, slowly add the wet ingredients to the dry ingredients. Once all the wet ingredients are added, continue to mix on low speed for 30 seconds. Scrape down the sides of the bowl and mix for another 15 to 30 seconds. Don't over beat this batter. It will be thin.

Combine the first measures of sugar (4 tablespoons) and water (3 tablespoons) in a small saucepan. Gently stir together until it feels like wet sand. Do the same thing with the second measures of sugar (6 tablespoons) and water (3 tablespoons) in another small saucepan.

Place both saucepans on the stove and begin to heat them up. Heat the first saucepan (the one with 4 tablespoons sugar and 3 tablespoons water) over medium heat. Heat the second saucepan (the one with 6 tablespoons sugar and 3 tablespoons water) over medium low heat. Heat the first sugar water mixture to 115 degrees C (239 degrees F), keeping track of the temperature with an instant-read or candy thermometer.

While the sugar is heating up, whip the egg whites in a stand mixer fitted with the whisk attachment. Whip until soft peaks form. If the egg whites reach medium soft peaks before the first sugar hits 115 degrees C (239 degrees F), slow your mixer down and let the sugar catch up. Or, if you notice that the sugar is nearly at 115 degrees C (239 degrees F) and the egg whites are still a ways from becoming soft peaks, turn the heat way down under the first measurement of sugar water. Ideally, you want the egg whites to reach a soft peak at the same time the sugar water hits 115 degrees C (239 degrees F).

Once the first sugar measurement reaches this temperature, remove it from the heat and very carefully pour it into the egg whites while the mixer is on low. 

When all of the sugar is successfully added to the egg whites, turn the mixer speed back up and turn the heat under the second sugar water mixture to medium. You know what this mixture of sugar water to reach 120 degrees C (248 degrees F). Once it reaches this temperature, remove it from the heat and very carefully pour it into the egg white mixture. Let the egg white mixture whip until cool. 

Once the egg white mixture has reached room temperature, turn the mixer off and fold in the peanut butter and chopped peanuts. Use immediately or store in the refrigerator in an airtight container. 

Mix sugar, water and corn syrup in a small saucepan.

Bring the water and sugar mixture to boil over medium heat, but DO NOT STIR. (Stirring encourages crystallization). Let the mixture cook until it caramelizes into a golden brown color. It happens quickly, so keep an eye on it.

Remove the caramelized sugar syrup from the heat and slowly mix in the cream. Pour in just a tiny bit at a time, especially at the beginning, and mix to combine. You can start adding more and more as you go along.

Mix in salt and vanilla. Stir to combine.

Set the caramel sauce to the side and let cool to room temperature before using.

Spread a small dollop of frosting on your cake board. Place the first cake layer on the board, with the shortbread cookie crust on the bottom.

Spread about half of the nougat filling on top of the cake layer. Make sure to get eye level with the cake to ensure it is level. Drizzle some of the salted caramel over the nougat.

Place the second cake layer, shortbread cookie crust on the bottom, on top of the nougat and caramel. Repeat step 2.

Place the final cake layer, shortbread cookie crust on the bottom, on top of the second layer of nougat and caramel. If the cake feels too unstable to crumb coat, place the naked cake in the freezer for about 15 minutes to set the fillings and stabilize the cake.

You'll then spread a thin layer of frosting around the entire cake to lock in any crumbs. This is called the crumb coat. Freeze the cake for 10 to 15 minutes to ensure the crumbs get locked into this coat of frosting. After the frosting is set, continue to frost the cake with the remaining peanut butter frosting.