Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a medium bowl, whisk together the flour, black cocoa powder, baking soda, baking powder, and salt. Set aside.
In a large mixing bowl, cream the softened butter and sugar together until light and fluffy, about 3-5 minutes.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Gradually add the dry ingredients to the butter mixture, alternating with the buttermilk. Start and end with the dry ingredients, mixing until just combined.
Carefully stir in the hot water until the batter is smooth.
Divide the batter evenly between the prepared cake pans.
Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cakes to cool in the pans for 10 minutes before transferring them to wire racks to cool completely.