Preheat oven to 350°F (176°C). Prepare three 8-inch cake pans with parchment paper circles in the bottom and grease the sides.

In a medium bowl, whisk together the flour, sifted cocoa powder, baking soda, and salt. Set aside.

In a large mixer bowl, beat together the butter, vegetable oil, brown sugar, and vanilla extract on medium speed until light in color and fluffy, about 2-3 minutes.

Add the eggs one at a time, mixing until mostly combined after each. Scrape down the sides of the bowl as needed.

Add the sour cream and mix until well combined. The batter may look a little stringy or separated, which is okay.

Add the milk and mix until well combined.

Add half of the dry ingredients to the batter and mix until mostly combined.

Carefully add half of the hot coffee and mix until well combined.

Add the remaining dry ingredients and mix until well combined and smooth. Scrape down the sides of the bowl as needed.

Add the remaining hot coffee and mix until well combined and smooth. Do not overmix the batter.

Divide the batter evenly between the prepared cake pans. Bake for 23-27 minutes, or until a toothpick inserted into the center comes out with a few crumbs.

Remove the cakes from the oven and let them cool in the pans for 2-3 minutes before inverting them onto cooling racks to cool completely.

In a large mixer bowl, beat the softened butter until smooth and creamy.

Add the melted and slightly cooled semi-sweet chocolate in three parts, mixing until well combined after each addition. This helps prevent chocolate chunks.

Add the cocoa powder and about half of the powdered sugar, and mix until well combined.

Add the salt and half of the heavy cream, and mix until well combined.

Add the remaining powdered sugar and mix until smooth.

Add the remaining heavy cream, a tablespoon at a time, as needed to reach your desired frosting consistency.

Once the cake layers are completely cool, use a large serrated knife to gently level the tops if they have domed.

Place the first cake layer on a serving plate or cake stand. Spread about 1 cup of frosting evenly over the top.

Add the second cake layer and spread another cup of frosting over it.

Place the final cake layer on top. Frost the entire outside of the cake with the remaining buttercream, smoothing it as desired.

Decorate the cake with additional chopped chocolate around the edges or as desired.

Serve and enjoy!