Step 1

Preheat oven to 350 degrees (F). Spray two 9-inch round baking pans with non-stick baking pray. Line the bottom of each pan with a round of parchment paper. Then spray the parchment paper with non-stick baking spray. Set aside.

Step 2

In a large bowl sift together the flour, cocoa powder, baking soda, baking powder, and salt. Set aside.

Step 3

In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl using a handheld electric mixer, beat the butter at medium speed until smooth, about 1 minute.

Step 4

Gradually add in both sugars, one at a time, and beat until the sugar has been incorporated into the butter. Then increase the speed to high and beat until the mixture is light and fluffy, about 4 minutes. You may need to stop the mixer and scrape down the sides and bottom of the bowl once in a while to ensure no butter is getting stuck.

Step 5

Add in the eggs and egg yolks, one at a time, beating well after each addition, and scraping down the sides and bottom of the bowl as needed. Add in the vanilla extract and beat until combined.

Step 6

In a spouted measuring cup, combine the oil and sour cream.

Step 7

On the lowest speed setting available, add the flour in three additions, alternating with the sour cream mixture, in two addition, beating until just combined! You should still see the lightest trail of dry ingredients when you stop the mixer.

Step 8

Pour in the hot coffee and let the mixture sit, undisturbed, for 30 seconds. Then, using a rubber spatula, gently stir until the batter is just evenly combined.

Step 9

Divide the batter evenly among the prepared pans (around 850 grams per pan) and smooth the tops with a rubber spatula.

Step 10

Bake in preheated oven for 38 to 45 minutes, or until a toothpick inserted into the center of a cake comes out clean, or with a few moist crumbs attached.

Step 11

Place the cakes, in the pans, on a wire rack and cool for 20 minutes. Then invert the cakes onto the rack and let cool completely, about 1 hour.

Step 12

Finely chop the chocolate using a large chef's knife. Place the chopped chocolate into the bowl of a stand mixer fitted with the whisk attachment.

Step 13

In a small saucepan heat the cream and corn syrup over medium-high heat until the mixture comes just short of a rolling boil. Remove the pan from heat and pour over the chopped chocolate.

Step 14

Allow the mixture to sit, undisturbed, for 2 minutes. Then, using a rubber spatula or metal spoon, gently stir until the chocolate is completely melted and the mixture is smooth and glossy. Stir in the vanilla.

Step 15

With the mixer on medium-speed, add in the butter, 1 tablespoon at a time, beating well after each addition, and not adding more until the first addition has been completely incorporated into the frosting. Beat in the salt.

Step 16

Refrigerate the frosting, loosely covered, for about 1 hour, or until it's firm enough to spread. Frosting may be made up to 24 hours in advance and stored, covered, in the fridge. You'll need to let it come to room temperature before using.

Step 17

Using a long, serrated knife, slice off the domed top of each cake layer so it is smooth and even. Then slice each cake in half horizontally, so that you have 4 even layers. Set all of the cake scraps aside, we'll use those later to decorate!

Step 18

Place one cake layer on a large plate or cake stand. Spread 1/2 cup of the frosting on top of the cake, covering it completely. Then top with another cake layer, and repeat the layering process, ending with the last cake layer on top. Spread all remaining frosting  over the top and sides of the cake.

Step 19

Using your hands, crumble up the remaining cake scraps until they're in fine crumbs. Pat the crumbs gently around the sides of the cake. You might have leftovers, which you may discard or enjoy as a snack!

Step 20

Allow the cake to set for 20 minutes before slicing. Then serve, or store, in the refrigerator, for up to 5 days. Bring to room temperature before serving!