Preheat your oven to 325 degrees F. Spray an 8×8 square inch cake pan with cooking spray, line with parchment paper, and spray again. Set aside.

In a stand sized mixer fitted with the paddle attachment, combine the flour, sugar, cocoa powder, baking soda, baking powder, and salt. Mix on low until evenly combined.

In a small bowl, whisk the eggs, buttermilk, hot water, vanilla extract, and vegetable oil until evenly combined.

With the mixer on the lowest speed, pour the liquid ingredients into the dry ingredients and mix just until combined. There should be no flour streaks. With a rubber spatula, scrape the bottom of the bowl to make sure the batter is evenly combined.

Add the the batter to the prepped pan, and carefully smooth the batter with a small offset spatula and bake until a toothpick comes out clean, or with only a few crumbs on it, about 35-40 minutes. Depending on your oven.

After they are out of the oven, I let mine cool for 15 minutes. Then I transfer the cake onto a wire rack to finish cooling in the fridge or freezer to help speed up the process. (20 minutes in the freezer, 30 minutes in the fridge)

While the cake is cooling, make the frosting.

In the bowl of electric mixer fitted with the paddle attachment, combine the butter and peanut butter. Beat on medium-high speed until smooth, about 2 minutes.

With the mixer on the lowest speed, add the powdered sugar, vanilla, salt, and cream to the bowl. Once mixed, beat on high for 3 minutes, scrape down the bowl and beat for 1 more minute. It should look light and fluffy.

Use a wooden spoon to mix frosting one last time to get rid of air bubbles.

In the bowl of a standing mixer, use a whisk to combine the eggs and salt until frothy, once frothy, keep the mixer on the lowest speed to keep the stabilized.

While the egg whites are whipping, in a small sauce pan, combine the sugar, corn syrup, water and vanilla over medium heat. You want the sugar to dissolved, so roughly 3-5 minutes.

Once the sugar has melted, turn the the mixer on medium-high speed, and slowly start to pour the hot sugar mixture on the mixing bowl’s inside rim, letting it run down the side of the bowl. Make sure to pour VERY slowly. If you do this correctly, you will temper your eggs, and not scramble them. This will take about 2 minutes.

Once all of the sugar has be added, turn the mixer up to high speed, and beat for about 5 minutes or until very stiff and shiny. (This does not hold well, so make sure to to use day of.

Once the cake has cooled (or chilled) and is no longer warm, using the peanut butter frosting, frost the top of the cake. To achieve this, I use a small offset spatula and a large cookie scoop to scoop 9 balls across the top. This help the frosting spread evenly.

Next add the marshmallow fluff and evenly spread, you might not use all of the marshmallow fluff, you can store the left over in a plastic bag and freeze it for up to 3 months,

Cut into 9-12 slices and serve!