Preheat oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan.
In a large bowl, whisk together flour, sugar, cocoa, baking soda, baking powder, and salt.
Add buttermilk, oil, eggs, and vanilla. Beat until well combined. Gradually add hot coffee and mix until smooth.
Pour batter into prepared pan and bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean.
Let cake cool completely before frosting.
To make the frosting, in a large bowl, cream together butter, powdered sugar, and cocoa until smooth. Gradually add milk and vanilla, beating until light and fluffy.
Frost the cooled cake. Cut into squares and serve.
Notes
Enjoy this delicious and easy Neiman Marcus Cake! Store in an airtight container at room temperature.