Preheat the oven to 350F degrees. Line the bottom of two 8 inch round cake pans with parchment paper and grease the sides of the pan. Set aside.
In a large bowl whisk together the flour, cocoa, baking soda, baking powder and salt for about 30 seconds.
In a separate large bowl using a hand-held or electric mixer on medium speed beat together the oil, sugars, eggs and vanilla until well combined (about 3 minutes). Turn down the mixer to low and beat in ½ of the buttermilk followed by half of the flour mixture. Repeat with the second half of the buttermilk and the rest of the flour mixture, turning off the mixer and scraping down the sides of the bowl with a rubber spatula as needed. Carefully add in the hot coffee beating on low speed until combined.
Pour the batter evenly between the two prepared cake pans and bake for 35-40 minutes until an inserted toothpick comes out clean. Allow the cakes to cool in their pans for at least 30 minutes before removing and continuing to cool on a wire rack.
To make the frosting in a large bowl using a hand-held or stand electric mixer beat the butter on medium speed until fluffy and no lumps remain (about 2 minutes). Add in the sour cream and melted chocolate and continue beating until well combined. Add in the cocoa powder, followed by the icing sugar about ½ cup at a time while scraping down the sides of the bowl as necessary. Finally, beat in the corn syrup, salt and 1 tablespoon of whipping cream at a time, adding more icing sugar as necessary.
To assemble the cake, place one cake on a plate or cake stand. Using a flat edge knife frost the top of the cake with approximately ⅓ of of the frosting. Place the second cake on top of the first. Frost the top of the second cake with a thin layer of frosting, followed by the sides of the cake with a thin layer. Finally, go over the top of the cake and sides with the remaining frosting to make a swirl pattern.