Preheat oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a large bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add buttermilk, oil, eggs, and vanilla extract to the dry ingredients. Beat until combined.
Gradually add hot coffee, mixing until batter is smooth. Batter will be thin.
Pour batter evenly into prepared pans. Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean.
Let cakes cool in pans for 10 minutes before inverting onto a wire rack to cool completely.
While the cake cools prepare the frosting. In a large bowl, beat the butter until smooth and creamy. Gradually add in the powdered sugar, beating until combined. Add the heavy cream and vanilla extract and continue beating until light and fluffy.
Once the cake is fully cooled, frost the top of one cake layer with frosting. Place the second cake layer on top of the frosting. Frost the top and sides of the second cake layer with the rest of the frosting.