Preheat your oven to 350°F (175°C) and grease two 8-inch round cake pans.

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

In a large mixer bowl, combine the sugar, eggs, sour cream, buttermilk, vegetable oil, and vanilla extract.

Gradually mix the dry ingredients into the wet mixture, alternating with hot water. Add chopped walnuts.

Divide the batter between the pans and bake for 28-32 minutes until a toothpick comes out clean.

Make the frosting by beating the butter, powdered sugar, cocoa powder, and heavy cream until fluffy.

Once cooled, frost the first layer of the cake, add walnuts, place the second layer, and frost the whole cake.

For the ganache, heat heavy cream and pour over chocolate chips, stirring until smooth.

Drizzle ganache over the frosted cake and sprinkle remaining walnuts on top.