Preheat your oven to 350℉. Prepare three 9-inch cake pans. Use a paper towel to rub shortening all over the inside of each pan, coating them completely. Cut a round of parchment paper to fit inside each. Place this on top of the greased pan bottom, then grease over the parchment paper. Add a handful of flour, and tap the pan around to evenly coat the entire inside with flour, tapping out the excess.

Add the hot water to a large glass measuring cup or bowl. Whisk in the cocoa & espresso powder until completely dissolved. Set aside. In a large bowl, whisk together the flour and sugars, breaking up any lumps of brown sugar as best you can. Then, whisk in the baking soda, baking powder, and salt. Check that the water & cocoa mixture is just lukewarm, and if it is, whisk in the oil, buttermilk, and vanilla. In one of the measuring cups you just dirtied that's now empty, add the eggs and lightly beat with a fork. Pour the cocoa liquid mixture and the lightly beaten eggs over the dry ingredients. Whisk gently to combine.

Divide the batter evenly among your three prepared pans. Bake at 350℉ for 24 to 28 minutes. A toothpick inserted into the center of the cake will pull out moist crumbs. Let cakes cool in the pans placed on wire racks for 10 minutes, then run a butter knife around the edges to loosen, and invert onto the cooling racks to cool completely while you make the frosting.

In a large mixing bowl or in the bowl of a stand mixer fitted with the paddle attachment, beat the butter until creamy, about 60 seconds. Beat in the peanut butter until creamed with the butter. Mix in the powdered sugar in a few additions, using heavy cream as needed to help it combine. Mix in the vanilla, and a pinch of salt. Taste and add more powdered sugar and/or salt if desired.

Spread a small dollop of frosting on your cake plate to secure the cake. Place the first cake layer on this, and place the cake plate on top of a cake turntable. Spread 1 and ½ cups of frosting over the layer. Place the second cake layer on top and spread any frosting 'overhang' between the two layers to seal them together. Chill for 5-10 minutes to set things so the layers don't slide around. Repeat with the second layer. Add the final layer upside down for a flat top, and give the cake a thin layer of frosting on top and on the sides. Pop the cake in the fridge for 20-30 minutes or until the frosting is set. Then, frost the top and sides of the cake sparingly with the remaining frosting.

Add finely chopped chocolate to a small bowl. Heat heavy cream in a small saucepan over medium high heat until simmering. Pour over the chocolate, let sit for 4 minutes, then stir until completely smooth. Add 1-3 tsp vegetable oil to get a smooth, pourable consistency. Set cake on a turntable. Pour the chocolate onto the center of the top of the cake, then spin the cake slowly while pushing ganache to the edges, and over, with an offset spatula to create drips. Let chill 20-30 minutes, until ganache is set. Use remaining frosting to pipe a border on top, if desired. Place peanut butter cups and chopped peanuts on the frosting as garnish.

Chill another 20 minutes or so to ensure the frosting you piped on last is set. Store leftover cake in the fridge in an airtight container or cake carrier.