The most delicious chocolate cake layers baked on a graham cracker, almond, coconut, and chocolate crust, with a custard filing and covered in a chocolate fudge buttercream.
Spray a three 8-inch round cake pans with nonstick spray, line the bottoms with parchment paper and spray again. Set aside.
In a double boiler, over medium heat, melt the butter. Once the butter is melted, turn the heat off and whisk in the sugar, cocoa powder and salt until combined.
While whisking vigorously, slowly pour in the beaten egg. Turn the heat back on to medium and cook until the mixture thickens slightly.
Remove the mixture from the heat completely and add in the graham cracker crumbs, coconut, and almonds. Toss to combine evenly.
Evenly divide the mixture between the three pans (about 6 ounces in each) and firmly press into place to create a crust.
Preheat your oven to 325 degrees F.
In a medium bowl, whisk together flour, salt and cocoa powder. Set aside.
In the bowl of a stand mixer, fitted with the paddle attachment, combine the butter and sugar. Beat on medium speed until light and fluffy, about 2 minutes. Scrape down the sides of the bowl and mix again for another minute.
Add the eggs, one at a time, being sure to mix and scrape down the sides of the bowl between each addition. Once all of the eggs are added, continue to beat on medium-high speed for about two mintues, until the mixture gets lighter in color and bigger in volume.
With the mixer on low speed, add 1/3 of the flour mixture, followed by 1 cup of the buttermilk. Continue with another 1/3 of the flour, the second half of the buttermilk and then the remaining flour mixture. Stir until combined.
In a small bowl, combine the vinegar and baking soda. The mixture will bubble. Add the mixture to the cake batter and stir on low until combined. Scrape down the sides of the bowl and mix again for another 20 seconds.
Fold in the sour cream until no streaks remain.
Divide the batter evenly between the prepared pans (20 ounces in each of the 8-inch pans). Bake for about 35-40 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs on it.
In a medium size mixing bowl, combine all of the ingredients and beat until smooth, about two minutes. The mixture should be fluffy and pale in color. If needed, add an additional tablespoon of heavy whipping cream to create a spreadable consistency.
In a food process, combine the butter, powdered sugar, cocoa and salt. Mix until smooth, about 30 to 60 seconds, scraping down the sides and corner of the bowl about half way through.
Add the corn syrup and vanilla, and mix until combined, about 30 seconds.
Scrape down the sides of the bowl and add the melted chocolate. Pulse until the mixture is smooth and creamy, about 30 seconds.
Place the first cake layer top side up, in the center of the cake board. Evenly spread half of the custard filling over the cake layer.
Place the second cake layer on top of the custard filling and spread the remaining filling over the cake layer.
Place the final cake layer, top side up, on the filling. Spread a thin layer of the chocolate fudge buttercream over the entire cake. Freeze the cake for 15 minutes. This is the crumb coat.
Once the crumb coat is set, continue frosting the cake with the remaining buttercream.