Make the Cake: Preheat oven to 350 degrees F. Grease three 8-inch round cake pans, line the bottoms with rounds of parchment paper, grease the parchment, then flour the insides of the pans, tapping out excess; set aside.
In the bowl of an electric mixer (or large mixing bowl if you're using a hand mixer), sift together the flour, sugar, cocoa powder, baking soda, baking powder and salt. In a medium bowl, whisk together the eggs, buttermilk, coffee, oil and vanilla.
Add the wet ingredients to the dry ingredients and mix for 2 minutes on medium speed. Scrape the sides and bottom of the bowl and mix for an additional 20 seconds (the batter will be very thin).
Divide the batter evenly among prepared pans. Bake for 20 minutes and rotate the pans in the oven. Continue to bake until a toothpick inserted into the center of one of the cakes comes out almost clean (with a few moist crumbs), about 12 more minutes. Cool the cakes (in the pans) on wire racks for 20 minutes, then carefully turn them out onto cooling racks to cool completely.
Make the Nougat Filling: Melt the butter in a medium saucepan over medium heat. Add the sugar and evaporated milk, stirring until dissolved, and bring to a boil. Reduce the heat to low and cook for 5 minutes, stirring occasionally. Remove the pan from heat and add the marshmallow fluff, peanut butter, and vanilla extract, stirring until completely smooth. Fold in the peanuts. Let the nougat mixture cool to room temperature before using it in the cake. You can do this leaving it at room temperature or you can pop it into the refrigerator to speed up the process. Be sure to give a stir occasionally as it cools.
Make the Frosting: Beat together the butter and cream cheese on medium-high speed for 5 minutes (I like to use the whisk attachment for my KitchenAid stand mixer, but it's not necessary). Pour in the salted caramel and beat until combined. Reduce the speed to medium-low and slowly add the powdered sugar, a little at a time, until it has all been incorporated. Increase the speed to medium-high and beat for an additional two to three minutes, until light and fluffy.
Assemble the Cake: If your cakes baked up uneven or have domed on top, level off the tops. Place one cake layer on a serving plate. Cover with half of the nougat filling and then spread a couple spoonfuls of the salted caramel sauce over top to evenly cover the nougat filling. Top with a second cake layer and cover with the remaining nougat filling and top with caramel sauce. Place the final cake layer on top face-down. Frost the cake with the salted caramel frosting, finishing it as smoothly as possible. Refrigerate the cake for at least 1 hour, until the frosting is set.
Make the Chocolate Ganache: While the cake chills, make the chocolate ganache. Place the chocolate in a medium bowl; set aside. Place the cream in a small saucepan over medium heat and warm until it just comes to a boil. Pour the cream over the chopped chocolate and let sit for 2 minutes. Begin whisking the mixture in the center, gradually working your way outward until the ganache is completely smooth. Set aside to cool, whisking occasionally, until it has thickened slightly, yet still a pourable consistency.
Garnish the Cake: Transfer the ganache to a 2-cup measuring cup. Slowly pour the chocolate ganache into the center of the cake, letting it push itself outward and flow over the sides of the cake. Refrigerate the cake for at least 30 minutes, giving the ganache a chance to set up. To finish garnishing, drizzle some additional salted caramel sauce over the top and side of the cake, and top with chopped peanuts. Keep the cake refrigerated, removing it from the refrigerator about 20 minutes prior to serving.