Preheat your oven to 350°F (175°C). Grease and line two 8-inch round cake pans with parchment paper.

In a large mixing bowl, sift together flour, sugar, cocoa powder, baking powder, baking soda, and salt.

Add buttermilk, vegetable oil, eggs, and vanilla. Beat on medium speed until smooth.

Slowly mix in the hot water until the batter is thin and well combined.

Divide the batter evenly between the prepared pans.

Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.

Let cakes cool in the pans for 10 minutes, then transfer to wire racks to cool completely.

To make the ganache, heat the heavy cream in a saucepan over medium heat until it just begins to simmer.

Pour the hot cream over the chopped chocolate in a bowl. Let sit 5 minutes.

Add butter and stir until smooth and glossy.

Let ganache cool slightly until it thickens to a spreadable consistency.

Place one cake layer on a serving plate, spread ganache on top, then add the second layer and cover the top and sides with ganache.