PEANUT BUTTER CAKE

1. Position a rack in the centre of the oven, and preheat to 350˚f / 180˚c. Spray and flour 3 six inch pans, or 2 eight inch pans.
2. In the bowl of a stand mixer fitted with the paddle attachment (or a large bowl using an electric hand mixer), beat together the butter, peanut butter, sugar, vanilla, baking powder, and salt at medium speed until fluffy and lighter in colour, stopping to scrape down the sides of the bowl with a rubber spatula to make sure there are no butter lumps, about 5 minutes. 
3. Add the eggs, one at a time, until completely combined. Stop and scrape down the sides of the bowl halfway through mixing and after adding the last egg. 
4. With the mixer on low, slowly add the flour to the butter mixture until just incorporated. Scrape down the sides of the bowl one last time. Fold in any remaining streaks of flour by hand. 
5. Divide the batter evenly between the prepared pans and bake, rotating the pans' positions halfway through baking, until a toothpick inserted in the centre of a cake comes out clean or with a few crumbs clinging to it, 40-50 minutes for 8-inch round pans or 30-35 minutes for 6-inch round pans. 
6. Transfer the cakes to a rack to cool in the pan for about 30 minutes. Turn the cakes out onto a flat surface, like plates or a clean counter top. Allow to cool completely before frosting, filling, or storing.

PEANUT BUTTER CRUNCH

1. Line a cookie sheet with heavy-duty aluminium foil and grease the foil with cooking spray.
2. In a medium saucepan, combine the syrup, water, and sugar. Cook over medium high heat until the mixture reaches 300˚f /150˚c on a candy thermometer or the hard crack stage, 10 to 15 minutes.
3. Remove the pan from the heat and immediately whisk in the peanut butter. Pour onto the prepared cookie sheet and smooth the top with a heatproof rubber spatula. 
4. Allow the nut butter crunch to cool completely before chopping into small chunks. Store in an airtight container until ready to use. 

DARK CHOCOLATE SWISS MERINGUE BUTTERCREAM

1. In a medium heatproof bowl, whisk together the egg whites, sugar, and salt. Heat the mixture in the microwave on high for 1 minutes at a time, whisking after each interval, until the sugar has dissolved, 2 to 3 minutes. Or, heat the mixture over a double boiler, whisking occasionally, until the sugar has dissolved. If you're using fresh egg whites, heat the mixture until it measures 160˚f / 71˚c on a candy thermometer. 
2. Pour the egg mixture into the bowl of a stand mixer fitted with the whisk attachment (or into a large bowl if using a hand mixer). Beat the egg whites on low speed just until the mixture starts to loosen and foam. Turn the mixer up to high speed and beat the egg whites until the mixture resembles a white, fluffy cloud, 8 to 10 minutes. 
3. Turn the mixer down to low speed and add the butter, a few cubes at a time. The mixture will appear curdled, but that's ok. Once all the butter has been added, turn the mixer up to medium high speed and beat until the buttercream is smooth, glossy, and light in colour, 10 to 15 minutes.
4. Add the vanilla extract and cooled melted chocolate and mix to incorporate.

ASSEMBLY

1. Level off the cooled cakes. Have your chopped peanut butter crunch and dark chocolate buttercream ready. 
2. Place the first levelled cake onto a turntable or cake stand. Spread generously with buttercream, then sprinkle a handful of peanut butter crunch over the buttercream. Top with the second layer of cake, and repeat the buttercream and nut crunch process. Place the final layer of cake on the top of the stack (I like to put this one upside down to give it a nice flat top). Crumb coat using buttercream, and leave to rest in the fridge for 15-20 minutes to firm up. Coat with a second coat of buttercream, decorating as desired - I went with a semi naked finish. Top with Extra peanut butter crunch. Serve at room temperature, and refrigerate any leftovers in an airtight container.