Preheat oven to 350°F (175°C). Coat four 8-inch cake pans with grease and line them with parchment paper.
In a bowl, combine flour, cocoa powder, sugar, baking soda, baking powder, and salt, then whisk thoroughly.
In another bowl, beat eggs, oil, sour cream, and vanilla until combined.
Gradually mix dry ingredients with wet, alternating with buttermilk.
Stir in hot coffee, then divide batter into pans.
Bake for 22–25 minutes, or until a toothpick inserted in the center emerges clean. Allow to cool completely.
For the frosting, whip butter until creamy, then blend in powdered sugar, cocoa powder, and salt.
Add melted chocolate, vanilla, and cream, whipping until smooth.
Assemble cake by layering frosting between each tier and covering the top.
Chill for 15 minutes, then slice and enjoy.