Preheat the oven to 350°F. Grease a 9x9 metal pan and line it with parchment paper.
In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt.
In a large mixing bowl, cream together the butter and sugar until fluffy. Add the eggs and vanilla, mixing until smooth.
Alternate adding the dry ingredients and buttermilk to the butter mixture, mixing until combined. Stir in the hot coffee.
Pour the batter into the prepared pan and bake for 48-52 minutes, or until a toothpick inserted into the center comes out clean. Let it cool completely.
For the Chocolate Fudge Frosting:
Melt the butter in a small saucepan over medium heat. Add the salt and cocoa powder, mixing until combined.
Sift in the powdered sugar and add the heavy cream gradually, mixing until smooth.
Once smooth, spread the frosting over the cooled cake and serve!