Set the oven to 350°F (175°C). Grease three 9-inches round cake pans, line the bottoms with parchment paper, and dust lightly with cocoa powder or flour. Set the pans aside.

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

Using a stand or hand mixer, beat the softened butter and granulated sugar on medium-high until light and fluffy this takes about 2 to 3 minutes. Add eggs one at a time, beating well after each addition. Stir in the vanilla extract.

Lower the mixer speed. Add half the dry mixture to the creamed butter, followed by the buttermilk. Add the remaining dry ingredients, and then pour in the hot coffee. Mix just until the batter is smooth. The batter will be thin this is normal.

Divide the batter evenly between the prepared pans. Place them on the center rack and bake for 30 to 35 minutes. Check with a toothpick it should come out clean. Let the cakes cool in the pans for about 10 minutes, and then turn them out onto wire racks to cool completely.

In a large bowl, beat the butter until creamy. Add cocoa powder and melted chocolate, mixing until smooth. Gradually beat in powdered sugar, alternating with heavy cream. Continue mixing until the frosting is fluffy and spreadable. Add vanilla and a pinch of salt, and beat another minute or two. Adjust consistency with more cream or sugar if needed.

Level the cooled cake layers if necessary. Place the first layer on a cake board or plate. Spread a generous amount of frosting over the top. Repeat with the next two layers. Cover the top and sides with the remaining frosting.

Place the assembled cake in the refrigerator for at least 30 minutes to help set the frosting. Let it sit at room temperature before serving to bring out the best texture and flavor. Slice and serve.