Preheat the oven to 350°F (175°C) and grease and line two 9-inch round cake pans with parchment paper.
Whisk together the flour, sugar, cocoa powder, baking soda, baking powder, and salt until well combined.
Add buttermilk, vegetable oil, eggs, and vanilla extract, then mix until smooth.
Slowly pour in the hot coffee or water while mixing until the batter is thin and glossy.
Divide the batter evenly between pans and bake for 30 to 35 minutes until a toothpick comes out clean.
Cool cakes in pans for 10 minutes, then transfer to wire racks to cool completely.
Beat butter, powdered sugar, cocoa powder, cream, vanilla, and salt until fluffy.
Frost the cooled cake layers and assemble, smoothing the top and sides as desired.